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1. For users operating in a good GNSS environment processing Is relatively straightforward provided the correct IMU Error Model has been chosen Fine static alignment is only practical for high accuracy IMUs and generally requires at least 10 minutes Kinematic alignment requires 4 8 seconds 20 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Process IMU Data The steps for processing IMU data are in the shaded box on Page 20 Plotting and Quality Control Once processing is complete view the quality of the results by analyzing the IMU plots Under the Output menu choose Results to access the following IMU plots Attitude Roll and Pitch This plot shows the roll and pitch profile of the processed IMU data Attitude Azimuth Heading This plot shows the heading azimuth of the IMU and the GNSS course over ground They should be in reasonable agreement If the red line and green line are 180 different then the IMU has been mounted backwards and a rotation of 180 about the Z axis will need to be entered under the Advanced tab of the IMU processing options Attitude Separation This plot requires that forward and reverse have both been processed It shows the difference between their attitude values and ideally they should agree IMU GNSS Position Misclosure This plot shows the difference between the GNSS only and the GNSS IMU trajectories and they should
2. 3 1 Data Formats In theory virtually any IMU sensor can be used with Inertial Explorer The only requirement is that the data be logged in the format provided below which allows easy decoding with IMU Data Conversion utility described in Section 2 1 1 on Page 49 The Table 2 in the shaded box presents the binary structure in which the conversion utility expects the raw IMU data to be logged Please contact Customer Service if you are unable to log data into the specified format 3 1 1 NovAtel s SPAN Technology With the use of NovAtel s SPAN technology note the difference in the IMU data decoding procedure Since the raw IMU data measurements are embedded into the same binary file containing the raw GNSS measurements only one step will be needed to separate the data and convert it into the Waypoint Group s format so the Raw IMU Data Converter utility does not need to be used Instead decode the GNSS and IMU data simultaneously via the Convert Raw GNSS data to GPB utility which can be accessed via File Convert When adding the measurement file to the Convert Files window for decoding ensure that the drop down menu under the Receiver Type box has been set to NovAtel OEM4 Then click either the Global Options or Options button to gain access to the IMU decoding settings Table 2 Binary Structure of Raw Data Description GpsTime 8 real time of the current IMU rate measurements in GPS
3. acos cos cos Inertial Explorer 8 20 User Guide Rev 6 73 Chapter 4 FAQ and Tips 4 5 How do I decode raw inertial data The raw IMU data decoder expects binary data in the format described in Section 2 1 4 on Page 51 The decoder needs to read an ASCII profile that defines which right hand sensor system the binary data has been stored in For example a given IMU might define a positive X axis as pointing out the front of the IMU box and a positive Z axis as pointing downwards The profile therefore must specify this in order to rotate the sensor axes into the Y forward Z up system that is used by Inertial Explorer The profile also needs to store values by which to scale the gyro output into degrees or degrees second The accelerometer data must be scaled to m s or m s 4 5 1 How do I deal with offsets between IMU sensor frame and vehicle body frame Ifthe IMU is typically mounted upside down you may wish to define a profile of your own so that Inertial Explorer automatically decodes your data in a way that does not require subsequent rotations to be applied during processing If the manufacturer s sensor system defines Z down as positive create a profile where Z up and X back are defined as being positive This produces a system in which the lever arms can be defined in the same manner as described in previous sections which is to say that the longitudinal axis of the vehicle body represen
4. Cancel Apply Forward Reverse Initial alignment whether processing forward or reverse determines the initial roll pitch and yaw of the IMU Alignment settings should be set with care to ensure that the best possible alignment is formed Method for Initial Alignment The following options are available and are largely dependent on the length of static data present Static coarse alignment only The data being used for alignment must be static as any motion results in an error Coarse alignment is performed for the first 30 to 120 seconds of static IMU data collection and is used as a seed value for attitude information for either fine alignment or navigation Coarse alignment uses the sensed gravity vector components to estimate roll and pitch It uses sensed Earth rotation rate to provide an initial estimate of the yaw of the IMU BI Most low accuracy sensors such as MEMS can measure gravity components but the Earth rotation rate which is roughly 15 arc seconds per second at the eguator may be masked by gyro noise As a result the initial yaw estimate from the coarse alignment may be wrong For applications involving constant GNSS updates coarse alignment is often enough to start kinematic IMU navigation Static coarse fine alignment Invoke if IMU is static for longer than 120 seconds lt Many high precision IMU applications recommend approximately 2 minutes of coarse alignment followed by 8 to 10
5. Chapter 4 4 8 1 How do I build my own error model This is not recommended for our typical user group Unless you have special equipment such as rate tables designed to provide exact motion and dynamics please realize that building an Error Model is a best guess iterative procedure You can do it but it is not an exact science by any means First of all based on the specifications of your gyros and accels try filling in reasonable standard deviation values for the initial estimates of the misalignments accel bias and gyro drifts These should be loose enough to allow the Kalman filter to move around until it can find a steady state but tight enough that the filter does not diverge Values here do not have to be too exact Typically make them somewhat larger than the manufacturers specifications and allow the filter to converge from there Spectral densities are a much less exact science The manufacturer should provide you with some ideas of the random noise on the gyros and accels These can be entered as starting points If the densities are too large the filter pays little attention to the IMU measurements and rely on the GNSS ZUPT DMI updates for all of its information content If the densities are too tight the update information is largely ignored Alternately to using information from manufacturer spec sheets you may wish to copy a profile from the manufact file and modify it to your own designs 4 8 2 How do I
6. Foreword Congratulations Congratulations on purchasing a Waypoint Products Group s software package Inertial Explorer is a Windows based suite of programs that provide GNSS Global Navigation Satellite System and inertial data post processing This manual will help you install and navigate your software Scope This manual contains information on the installation and operation of Waypoint Products Group s Inertial Explorer software package It allows you to effectively navigate and post process GNSS IMU Inertial Measurement Unit and wheel sensor data It is beyond the scope of this manual to provide details on service or repair please see the Conventions and Customer Service section on this page for customer support How to use this manual This manual is based on the menus in the interface of Waypoint s software It is intended to be used in conjunction with the most recent revision of the GrafNav GrafNet User Guide found at http www novatel com products waypoint grafnav htm and the corresponding version of Waypoint s Inertial Explorer software Prerequisites To run Waypoint software packages your personal computer must meet or exceed this minimum configuration Operating System Windows 2000 XP or Vista Hard Drive Space 75 MB of available space on the hard disk Processor A Pentium or Xeon processor is required Simultaneous forward reverse processing is possible on dual CPU and Xeon systems At least 2
7. azimuth degrees for forward and reverse alignment INITIAL_INS_POSITION latfwd lonfwd htfwd latrev lonrev htrev INS position for forward and reverse processing in DMS DMS m INITIAL_POSITION_SOURCE source 0 JCMB FWD REV 1 manual entry of position INITIAL_VELOCITIES vefwd vnfwd vhfwd verev vnrev vhrev If known input initial East North Up velocities m s for forward and reverse alignment INS_BODYFRAME_OFFSETS roll pitch yaw Constant angular offsets in degrees from the IMU axes to vehicle body frame axes INS_DATAGAP_TOL Num_consectutive_epochs_missing Exit on a single data gap that is larger than this number INS_FILE_NAME filename Name of IMU binary measurement file INS GPS TIME FRAME GPS TIME FRAME RCVR TIME FRAME GPS TIME FRAME i e revr time revr clock bias RCVR TIME FRAME i e nominal rev time INS LOWPASS 0 1 Use 1 for low pass filter on raw data INS PROCESS DIR FORWARD REVERSE FORWARD REVERSE direction INS processing INS_PROCESS_MODE mode GPS_INS or INS_ONLY INS_TIMERANGE start end Indicates IMU processing time range and whether to process ALL or PARTIAL INS_TYPE type LTN90 LRF 3 LN200 HG1700 JAMI IMU GENERIC IMU imr INS VERBOSE ON OFF Writes extra messages to FIL and RIL files MISALIGNMENT NOISE sd1 sd2 sd3 Spectral density of misalignment states in arcsec s MISALIGNMENT SD esddev nsddev hsddev A priori Kalman standard deviations for East North Up
8. seconds of the week GyroX 4 long scaled X body axis gyro measurement as anangular increment or angular rate GyroY 4 long scaled Y body axis gyro measurement as anangular increment or angular rate GyroZ 4 long scaled Z body axis gyro measurement as anangular increment or angular rate AccelX 4 long scaled X body axis accel measurement as a velocity increment or acceleration AccelY 4 long scaled Y body axis accel measurement as a velocity increment or acceleration AccelZ 4 long scaled Z body axis accel measurement as a velocity increment or acceleration t NovAtel OEM4 OEMY Options General IV Make all epochs Kinematic I Be compute position and clock offset IV Report L2 cycle slips IT Verbose messaging mode I Ignore measurement validity check phase party IV Write new GPB format I Do not create station file sta IV Create trajectory file fsp from following record Automatic E IT Create separate file for each MARKNTIME record GLONASS PRN offset 37 Use 45 for Topcon L2C phase correction 05 cycles m SPAN IMU IV Extract inertial SPAN data if available Convert Profile Automatic bd r Distance Measurement Unit DMI Wheel Circumference 1 96 m I Set tick counts per wheel revolution Tick counts per wheel revolution 2000 ticks Advanced Time tolerance for synchronizing BESTPOS and RANGE 5 00 seconds I Show DEMY rec
9. see Message Logs 59 FTM File see Trajectory File 60 G GNSS updates Using 31 H Heave applying 35 HMR File 58 format and description 58 l IMR File converting to 49 format and description 54 IMU Process loosely coupled setting 24 Process tightly coupled settings 38 IMU file adding to Inertial Explorer 23 Inertial Frame description 63 In Motion Kinematic Alignment description 29 89 Index Installation 19 K KAR ARTK New features 10 Kinematic Alignment See Alignment 69 L lever arm solve values 25 lever arm offset IMU to alternate sensor 45 IMU to GNSS 25 read values 25 loading existing solutions 43 Loosely coupled Processing 24 M manufacturer files downloading latest files 47 Message Logs format and description 59 Mount tab 33 N Navigation Frame description 64 NovAtel SPAN Data 53 p plots IMU data 44 list of Inertial Explorer plots 44 Plotting 21 Attitude 21 Processing discussion 65 Processing IMU options 24 Processing Profiles GNSS IMU 24 processing window 46 Project Wizard 22 steps 22 Q quick start 19 R Remote File Adding 22 RIL File see Message Logs 59 RIM File see Trajectory File 60 rotation sensor frame to body frame 33 RTL File 90 see Message Logs 59 RTM File see Trajectory File 60 RTS Smoother options 39 S Smoother see RTS Smoother 39 Static Alignment See Alignment 68 System tab 24 process IMU data 20 T Tightly cou
10. this module only supports omega primary angles 4 4 8 Where is my boresighting file data stored Everything related to the boresighting module is stored in a BSI file This file is ASCII but should not need to be modified 4 4 9 What if Inertial Explorer does not support my grid system If you are using a grid system not supported by Inertial Explorer then convert the roll pitch and heading values used to omega phi and kappa using the formulation described in Section 4 2 How are Inertial Explorer and coordinate frames related fe Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 4 4 10 What mathematical equations are used by boresighting The following is meant to provide information regarding the equations used by the boresighting module The photogrammetric equation is typically presented as Equation 1 in the box The boresighting feature solves for a rotation cam required in the derivation of the E matrix which represents the attitude of the image coordinate system with respect to the ground coordinate system This matrix is defined through Equation 2 in the box Inertial Explorer s boresighting module provides od the rotation angles that form the matrix Rw The other rotation matrix Reg is computed from Equation 3 in the box In this equation R accounts for the different axes definition between the camera and the IMU In general when a conventional image frame
11. 22 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 1 3 4 Add IMU File When starting a new project the program needs the data collected from the IMU The IMU file must be in the IMR format before being added 1 3 5 Convert Raw GNSS to GPB If data is logged without using Waypoint s logging software it will have to be converted to GPB format for processing Refer to Chapter 8 of the GrafNav GrafNet Version 8 20 Manual Raw IMU Data to Waypoint Generic IMR IMU data must be converted to IMR format in order to be processed by Inertial Explorer Use this utility to perform this conversion See Section 1 2 on Page 19 for help GPB to RINEX This produces a RINEX file from GPB files and supports the creation of Version 2 0 and 2 1 of the RINEX format For additional information refer to Chapter 8 of the GrafNav GrafNet Version 8 20 Manual 1 3 6 Removing Processing Files This removes all the files associated with any given project Refer to Chapter 2 of the GrafNav GrafNet Version 8 20 Manual for details of this utility Inertial Explorer capabilities are discussed here Files to Remove Selects files to remove from the project or folder Inertial Processing Removes all ASCII and binary files created during IMU processing including message logs and trajectories Inertial Smoothing Removes all ASCII and binary files created during smoothing How to start a new
12. AND LIABILITY Warranty Period Products 1 year Accessories 90 days in each case from the date of invoice NovAtel warrants that during the Warranty Period that a the Product will be free from defects in material and workmanship and conform to NovAtel specifications b the software will be free from error which materially affect performance and c if applicable as defined in the User s Manual be eligible for access to post contract support and software updates when available THESE WARRANTIES ARE EXPRESSLY IN LIEU OF ALL OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING WITHOUT LIMITATION ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE NOVATEL SHALL IN NO EVENT BE LIABLE FOR SPECIAL INDIRECT INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND OR NATURE DUE TO ANY CAUSE Q L Purchaser s exclusive remedy for a claim under this warranty shall be limited to the repair or replacement at NovAtel s option and at NovAtel s facility of defective or nonconforming materials parts or components or in the case of software provision of a software revision for implementation by the Buyer All material returned under Inertial Explorer 8 20 User Guide Rev 6 17 warranty shall be returned to NovAtel prepaid by the Buyer and returned to the Buyer prepaid by NovAtel The foregoing warranties do not extend to i nonconformities defects or errors in the Products due to accident abuse misuse or negligent use of the P
13. Buyer and returned to the Buyer prepaid by NovAtel The foregoing warranties do not extend to i nonconformities defects or errors in the Products due to accident abuse misuse or negligent use of the Products or use in other than a normal and customary manner environmental conditions not conforming to NovAtel s specifications or failure to follow prescribed installation operating and maintenance procedures ii defects errors or nonconformities in the Products due to modifications alterations additions or changes not made in accordance with NovAtel s specifications or authorized by NovAtel iii normal wear and tear iv damage caused by force of nature or act of any third person v shipping damage vi service or repair of Product by the Purchaser without prior written consent from NovAtel vii Products designated by NovAtel as beta site test samples experimental developmental preproduction sample incomplete or out of specification Products viii returned Products if the original identification marks have been removed or altered or ix Services or research activities THE WARRANTIES AND REMEDIES ARE EXCLUSIVE AND ALL OTHER WARRANTIES EXPRESS OR IMPLIED WRITTEN OR ORAL INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE ARE EXCLUDED NOVATEL SHALL NOT BE LIABLE FOR ANY LOSS DAMAGE EXPENSE OR INJURY ARISING DIRECTLY OR INDIRECTLY OUT OF THE PURCHASE INSTALLATION OPERATION USE OR LIC
14. Coarse Alignment Succeeded on attempt 1 This message appears at the beginning of forward reverse processing It indicates that the coarse alignment was successful Reading GrafNav Record 1000 Scanning the GPS IMU data before processing Warning Coarse Alignment has used up all of the Align Time Will Continue Processing anyway This message indicates that the INS processor used all the coarse alignment time entered Warning GUPT Missing in GPS data gt DT 0 200 This message indicates the presence of a gap in GPS data of time DT seconds As a result the processor cannot use this time as a GPS update Warning Trace of Body Earth matrix lt 0 after update Check on Fix 1 tr C of transform matrix 0 056389 This message is purely a mathematical computation warning Inertial Explorer 8 20 User Guide Rev 6 59 Chapter 3 Data and File Formats 3 3 2 FIM RIM FTM RTM Files This is the output format common to other Waypoint output files The first line of the output file always begins with OUTREC and is followed by the version number the processing engine and the type of output An example is given below as the first line SOUTREC Ver7 50 2531 INSDLL Forward InsOutput The output format is the following Out Tim InsGpsTime InsCorrTime GpsWeekt GPS seconds of week Geo latitude longitude ins ht ins DMS DMS m Loc d eastd northd htvel eastvel north vel up m m m m s m s m s Var Cee C
15. Range NovAtel SPAN users do not need this procedure because the IMU and GNSS logs automatically Before the IMU data can be processed establish a processing time range To do this find the first and last epochs of IMU data with concurrent GNSS data The IMU sensor might not be configured to start and stop collecting data at the same time as the GNSS receivers Entering the correct value is always preferable to solving 4 Select an error profile under the Error Model tab From the list that appears select the one corresponding to the IMU being used Click OK to begin processing The steps to determine processing time ranges are in the shaded box Determine Alignment Method Once the GNSS data is processed use the File Data Coverage plot in conjunction with the Velocity Profile plot to decide which alignment mode to use A static coarse alignment of two minutes in both directions is preferred for optimal processing If no static data is present at the start and or end times of the Velocity Profile plot then perform kinematic alignment instead For static alignment this plot helps to determine how much time is available for the processor to use The amount of time for the alignment can be set under the Forward and Reverse tabs via Process Process IMU The correct time length must be assigned because any movement during the static alignment results in an error
16. circumstances or causes beyond its ability to reasonably control Title shall pass to Purchaser when Purchaser has paid NovAtel all amounts due Risk of loss damage or destruction shall pass to Purchaser upon delivery to carrier Goods are provided solely for incorporation into the Purchaser s end product and shall not be onward delivered except as incorporated in the Purchaser s end product 4 COPYRIGHT AND CONFIDENTIALITY Copyright in any specification drawing computer software technical description and other document supplied by NovAtel under or in connection with the Order and all intellectual property rights in the design of any part of the Equipment or provision of services whether such design be registered or not shall vest in NovAtel absolutely The Buyer shall keep confidential any information expressed or confirmed by NovAtel in writing to be confidential and shall not disclose it without NovAtel s prior consent in writing to any third party or use it other than for the operation and maintenance of any Equipment provided GENERAL PROVISIONS All Purchase Orders are subject to approval and acceptance by NovAtel Any Purchase Order or other form from the Purchaser which purports to expand alter or amend these terms and conditions is expressly rejected and is and shall not become a part of any agreement between NovAtel and the Purchaser This agreement shall be interpreted under the laws of the Province of Alberta 6 LIMITED WARRANTY
17. file 3 Under the IMU Profiles box select the appropriate IMU type 4 Click Convert to create the IMR file See Chapter 2 on Page 49 for help 5 Add the file to the project via File Add IMU File How to determine processing time range 1 Select Output Plot Results 2 Load the File Data Coverage plot 3 View the time line for GNSS and IMU data acquisition and find the time range that has an overlap 4 Right click the desired time and select Set IMU Processing Time Start or End depending on the direction being processed How to process IMU Data 1 From the Process menu click Process IMU 2 Double check the processing time range under the General tab and the alignment settings under the Forward and Reverse tabs 3 Under the System tab enter the 3D lever arm offset from the IMU sensor to the GPS antenna If this offset is unknown then enable the Solver lever arm values as additional Kalman filter states option Convert and Process GNSS Data Refer to the GrafNav GrafNet 8 20 Manual to process GNSS data The only exception is that the new project is created in Inertial Explorer not GrafNav Convert IMU Data IMU data must be converted to Waypoint s generic IMR format for processing To do this follow the steps in the shaded box NovAtel SPAN users don t have to follow these steps because they have a one step process to convert their IMU data Determine Processing Time
18. for conversion to IMR format 3 Add base station data to project You can add your own local base station data in raw or GPB format or you can have the Wizard download free service data from the Internet If you plan to process with PPP you can skip the previous step and download the precise satellite clock and orbit files from the Internet How to start a new project using Auto Start 1 Enter a name for the project with File Name Check that the file path is pointing to the directory where the project files are saved 2 Choose the Master Station File s This is the GNSS data file collected at the reference station Raw GNSS data files must first be converted to Waypoint s common format GPB Refer to Chapter 8 of the GrafNav GrafNet Version 8 20 Manual for more information on converting data 1 3 File Menu Refer to the GrafNav GrafNet 8 20 Manual for information on the features available via this menu The points relevant to Inertial Explorer are discussed in this section of the manual 1 3 1 Project Wizard The Project Wizard offers you a guided step by step way of creating a project These Project Wizard steps are listed in the shaded box Auto Start Auto Start prompts for all the information required to process IMU data This option adds reference and remote stations and allows a project setting that best suits the application New Project To have Auto start
19. frame of reference An inertial coordinate frame does not rotate or accelerate with respect a to space fixed system of reference Accelerometers measure change of velocity with respect to an inertial frame while gyroscopes measure change of rotation with respect to inertial space and they are referred to as inertial sensors If measurements made in this inertial frame can be related to some chosen navigation frame then inertial sensors can be used to realize both 3 D coordinates X Y Z and 3 D attitude roll pitch and yaw in a manner that makes sense to navigators Figure 2 illustrates the relationship between the coordinate frames used by Inertial Explorer Figure 2 Coordinate Frames in Inertial Explorer The inertial computation navigation ei and body P frames are all portrayed here Keep Figure 2 in mind during the following discussion 4 2 1 What is an inertial frame A practical implementation of an inertial reference frame I frame is to define the centre of mass of the Earth as the origin The Z axis of this system goes through the poles and is coincident with the spin axis of the Earth The X axis is tied to an astronomical system and points at the vernal equinox which is defined as being the point where the apparent Sun crosses the celestial equator in the spring The Y axis completes a right hand triad This system is often referred to in literature as the Right Ascension system It is assumed that
20. may indicate a bad INS solution whereas separations nearing zero confirms the GPS solution This plot shows the difference between the GNSS IMU GPS calculated velocity and the mechanized INS Velocity velocity obtained from the GNSS INS processing Misclosure Another good analysis tool used to check INS stability Heads This plot is the difference between the IMU heading COG 9 and the GNSS course over ground values Effects difference of crabbing shows up as a direct bias in this plot Ke IMU Plots the raw accelerometer and gyroscope Values measurements from the IMU for all three axes Inertial Explorer 8 20 User Guide Rev 6 45 Chapter 1 Inertial Explorer 1 9 Interactive Windows Refer to the GrafNav GrafNet Version 8 20 Manual for information regarding the Map Window and the features available within it Only the additional information available through Inertial Explorer regarding the Processing Window are discussed here 1 10 Processing Window Table I on Page 44 contains a list of the additional parameters available for viewing in Inertial Explorer during processing Display these values via the View button in the Processing Window The values in the GrafNav GrafNet Version 8 20 Manual differs in the manners in which they are computed depending on the mode of processing being performed If the GNSS is being processed then the values displayed are those computed in the Kalman filter However during the I
21. minutes of any given mission should concern itself with static and kinematic alignment 4 3 5 What is IMU Kalman filtering The IMU Kalman filter consists of three misalignment states three position states three velocity states three gyro bias states and three accelerometer bias states The first nine states are in the ECEF computation frame They represent estimated errors in the realization of an ECEF computation frame from measurements made in the arbitrary vehicle body frame The sensor biases are lumped states accounting for constant and time dependent gyroscope and accelerometer measurement errors This filter runs in conjunction with equations which mechanize the IMU rate data meaning they propagate the attitude matrix and integrate coordinate differences between GNSS updates Inertial Explorer 8 20 User Guide Rev 6 69 Chapter 4 FAQ and Tips Table 3 Pitch and Yaw Differences Attribute Order of angles Direction of rotation Ground coordinate system Direction of rotation Roll pitch yaw Omega phi kappa Yaw pitch roll Omega phi kappa Air to ground Ground to air Geographic local level Normally a grid but may also be geographic Air to ground Ground to air For loosely coupled GNSS data must be processed first This produces FWD and REV files as well as a CMB file which represents the weighted mean of the forward and reverse GNSS proces
22. of its obligations hereunder where such breach is irremediable or if capable of remedy is not remedied within 30 days of notice from NovAtel requiring its remedy then and in any event NovAtel may forthwith by notice in writing terminate this Agreement together with the rights and licences hereby granted by NovAtel Licensee may terminate this Agreement by providing written notice to NovAtel Upon termination for any reasons the Licensee shall promptly on NovAtel s request return to NovAtel or at the election of NovAtel destroy all copies of any documents and extracts comprising or containing the Software The Licensee shall also erase any copies of the Software residing on Licensee s computer equipment Termination shall be without prejudice to the accrued rights of either party including payments due to NovAtel This provision shall survive termination of this Agreement howsoever arising 6 Warranty NovAtel does not warrant the contents of the Software or that it will be error free The Software is furnished AS IS and without warranty as to the performance or results you may obtain by using the Software The entire risk as to the results and performance of the Software is assumed by you See product enclosure if any for any additional warranty 7 Indemnification NovAtel shall be under no obligation or liability of any kind in contract tort or otherwise and whether directly or indirectly or by way of indemnity contribution or otherwise howsoe
23. terms of the X right direction Y forward direction and Z up direction of the INS body Gyro Drift Rate This is the apparent change in angular rate over a period of time as computed by the GNSS INS Kalman filter The effects are usually random It is plotted in terms of the X right direction Y forward direction and Z up direction of the INS body Generally they should stabilize after the alignment period and agree when processed in both directions Gyro Attitude This plots shows the misclosure residual of gyroscope Kalman filter updates Large values here could be an Misclosure indication of attitude instability IMU Angular This plot shows the gyroscope rate of change of attitude in Rates 9 the X Y and Z axes ofthe IMU body with the drift removed This plot is used to check the gyros Continued on the next page 1 6 Settings Menu Refer to Chapter 2 of the GrafNav GrafNet Version 8 20 Manual for information regarding all of the features available via this menu Only those features exclusive to Inertial Explorer are discussed here 1 6 1 IMU Settings This option provides access to the IMU processing settings without starting processing Data processing can only be engaged via the OK button under Process Process IMU See Section 1 5 on Page 24 fora complete description of all the settings available here 1 7 Output Menu Refer to Chapter 2 of the GrafNav GrafNet Version
24. the GNSS antenna Inertial Explorer 8 20 User Guide Rev 6 25 Chapter 1 Inertial Explorer IMU Processing Settings DMI Mount Error Model User Cmds 21 xi System General Forward Reverse GNSS Advanced File Info IMU file CAD sta InertislExploren IMU SPAN_AGSS imr Info IMU Time Range I Process all IMU data Begin time 164254 00 Process I Process IMU data only I Use GNS fend times End time fi 68820 00 IV Output binary values for smoother r Interval Data Rate Settings IMU raw data rate 100 0000 Hz V Extract from IMR header GNSS update interval 1 000 fs 1 Use every GNSS epoch 1 000 is IV Use GNSS update interval Binary high res output rate 4100 0 Ha IV Use IMU raw data rate ASCI Kalman output IMU Time Range Process All IMU Data If this option is enabled the software obtains the beginning and end times from the raw binary IMU file These times are in GPS seconds of the week for typical GPS time tagged applications Use GNSS start end times When selected IMU processing will start and end based on a time range set under the General tab of the GNSS processing options menu Begin Time For forward processing this time should correspond to a time in the trajectory files created during GNSS processing If it is then Inertial Explorer uses the GNSS derived position at that time to seed the inertial processing The ti
25. the data collection process Proper synchronization is vital Otherwise the IMU data will not process In NovAtel s SPAN system IMU data is automatically synchronized and the Inertial Explorer s GNSS decoder automatically extracts the IMU data This manual assumes the use of the GrafNav GrafNet 8 20 Manual you can request a copy from Customer Service or download it from our web site at www novatel com 1 2 Getting Started with Inertial Explorer This section provides a step by step procedures on how to process data in Inertial Explorer Installation Verify that the installation was successful by ensuring that you have a Waypoint Inertial Explorer program group on your computer If this program group is not there refer to the GrafNav GrafNet 8 20 Manual for installation instructions 19 oe mem See Ad pas Wei ms BERGE EAT OE FIKSES am WAYPSEINT How to start Inertial Explorer 1 Verify installation 2 Click on Inertial Explorer to start the program MY For NovAtel SPAN be sure that the Extract inertial SPAN data option is enabled in the OEM4 decoding options so that Waypoint s generic IMR raw IMU data file is created automatically Inertial Explorer 8 20 User Guide Rev 6 Chapter 1 Inertial Explorer How to convert IMU data 1 Open the conversion utility via File Convert Raw IMU Data to Waypoint Generic 2 Click the Browse button to locate the raw IMU data
26. 0 00 s Fine Jm fs Total 60 00 H Source of GNSS Updates Update data GNSS Combined missing x Browse External EADocuments and Settings nfoss Desktop Desktop Airbor File name ER DMI Mount Error Model User Cmds System General Reverse GNSS Advanced m Method for Initial Alignment Forward C Static coarse fine alignment C Transfer alignment enter known attitude Enter Attitude Kinematic alignment Initial Position and Velocity e Determine from GNSS suggested Use entered values IMU only using trajectory m Initial Static Alignment Period Coarse 60 00 s Fine 0 00 s Enter Total 60 00 s m Source of GNSS Updates Update data GNSS Combined missing Mi Browse External CAD ocuments and Settings nfoss Desktop Desktop Airbor File name Cancel Apply Inertial Explorer 8 20 User Guide Rev 6 29 Chapter 1 Inertial Explorer IMU Processing Settings 2 x DMI Mount System General Forward Method for Initial Alignment Error Model User Cmds Reverse GNSS Advanced atic coarse fine alignmen C Transfer alignment enter known attitude C Kinematic alignment Enter Attitude r Initial Static Alignment Period gt r Initial Position and Velocity Ze Determine from GNSS suggested 60 00 Sec s C Use entered values IMU only Fine 0 00 s using trajectory Total 60
27. 00 s Br of GNSS ene Update data gnss Combined missing i Browse EADocuments and Settings nfoss Desktop Desktop Airbor File name Cancel Apply IMU Processing Settings 2 x DMI Mount System General Forward Reverse Error Model User Cmds GNSS Advanced m Variance Factors for residuals Extra GNSS Updates GPS Position 2 0 I Enable Noisy Phase Measurements fi 0 0 IV Enable Heading Updates from File EEG Browse Std Dev Heading deg IV Enable GNSS velocity update Phase Meas fi 00 0 0 000 0 000 Boresight Rotation Z deg Cancel Apply Initial Position and Velocity There are two options available here Determine from GNSS This method is for collected GNSS data in addition to IMU data The starting position and velocity is read in from the GNSS trajectory specified under the Source of GNSS Updates box Use entered values This option is for performing IMU only processing If GNSS data has been processed load the position from a computed trajectory Otherwise enter it manually In either case click the Enter Position and Velocity button to access the input window Source of GNSS Updates Use this option to manually select the GNSS trajectory file from which Inertial Explorer obtains updates In most cases the CMB file is suggested or specify an alternate file by selecting External trajectory from the drop down menu and clicking the Bro
28. 000e 004 metres s 2 Gyro Drift 2 7778e 006 2 7778e 006 27778006 deg s rm Spectral Densities Values square root of Misalignment 2 7778e 004 2 7778e 004 27782004 deg s Accel Bias f3 1623e 006 f3 1623e 006 3 1623e 006 metres s 2 Gyro Drift 8 7841e 010 87840010 87842010 deg s Foo oen Kmec m s kaecng aaen ac m Velocity Position Cancel Apply How to create a custom profile Click the Add From button which allows for the creation of a new model based on a default model or click the Edit button which accesses the default models Generally the former method is recommended because it allows the default models as provided by the manufacturer to remain available for future use DI In either case disabling the Lock selection setting is required before the selection of any error model can be made Once an error model has been selected this setting should be re enabled to ensure that it is not accidentally changed Initial Standard Deviation Values The following mathematical quantities are available Misalignment These terms pertain to the difference between the computed direction cosine matrix and relate the IMU body frame to the computation frame ECEF in Inertial Explorer and an error free idealized direction cosine matrix or attitude matrix These values represent the best estimate of the sensor s ability to compute roll pitch and yaw during coarse
29. 005 6 59158e 005 1 76638e 004 8 14676e 005 8 67355e 005 6 86044e 05 Bia 1 52573e 003 9 69194e 004 1 84882e 003 6 70535e 004 7 98037e 004 4 89097e 04 Ecf 27963 018 15450 018 19782 767 Kal 0 0 0 4 0 4 0 002 0 000 0 000 0 001 0 000 0 000 Mis 0 003 0 001 0 001 0 000 0 000 0 000 209 687 170 538 Acc 2 633 0 852 0 692 60 Inertial Explorer 8 20 User Guide Rev 6 Data and File Formats Chapter 3 Ang 1 2924 2 6196 3 8727 Fli U 3 Flg KF 90 Rms 0 0280 0 750 0 000 0 089 Sta 1 0 000600 1 25 1 35 0 94 0 96 3 3 3 BIF BIR BTF BTR Files The data structure used for these binary files appears below typedef struct double phi lamda float ht plh type typedef struct double x y z xyz type typedef struct float x y z fxyz type typedef struct signed long iRoll iPitch iYaw iatt type typedef struct char Str 16 long HdrSize long IsExtended long RecSize long Reserved1 double Interval char ProgramName 32 char VersionName 32 char Direction 16 char Reserved2 392 imu hdr type holds latitude longitude and height degrees metres sf 1 0e SIMUOUT see IMU HDR STR above size of this header true if exended format used use later size of this record for later zero data interval s program name that created this file version that produced file Forward Reverse or Combined rese
30. 0e 004 metres s 2 27780006 277780006 277780005 deg rm Spectral Densities Values square root of Misalignment 27782004 27780004 27782004 deg s 3 1623e 006 3 1623e 006 3 1623e 006 metres s 2 87841e010 8 7841e 010 878416010 deg s aen Kmec kam mvs kaocn ro00ee 003 sc m Accel Bias Gyro Drift Accel Bias Gyro Drift Velocity Position IMU Processing Settings 21 System General Forward Reverse GNSS Advanced DMI Mount Error Model User Cmds r List of User Added Commands Meer Delete Clear r Edit Command Info Command Value s multiples separated by spaces v Format N A Usage N A Desc Enter command and its values Add Update New Entry x Settings Process direction Both Forward C Reverse User Me r GPS IMU Project Configuration IMU Settings Apply GNSS Settings Cancel Velocity Velocity spectral densities are noise densities that account for unmodeled velocity effects during each Kalman prediction Increasing this value permits more emphasis to be placed on the GNSS update data but may also lead to an increase in error growth during outages For this reason these values should be determined as part of the tuning process The default values are recommended unless dealing with a trajectory of unusually high dynamics such as a race car in which case these m
31. 56 MB of RAM is also required Although previous experience with Windows is not necessary to use Waypoint software packages familiarity with certain actions that are customary in Windows will assist in the usage of the program This manual has been written with the expectation that you already have a basic familiarity with Windows Conventions and Customer Service This manual covers the full performance capabilities of Inertial Explorer 8 20 data post processing software Simple conventions in this manual include the following lt This is a notebox that contains important information before you use a command or log or to give additional information afterwards This manual contains shaded boxes on the outside of the pages These boxes contain procedures screen shots tables and quick references If the software was purchased through a vendor please contact them for support Otherwise for software updates and customer service contact NovAtel s Waypoint Products Group using the following methods Call 403 295 4900 Fax 403 295 4901 Email wpsupport novatel com Web http www novatel com Write NovAtel Inc Customer Service Department 1120 68 Avenue NE Calgary AB Canada T2E 8S5 Inertial Explorer 8 20 User Guide Rev 6 9 What s New Inertial Explorer Version 8 20 New Features Project Wizard The new Project Wizard allows users to easily step through the process of creating a new project The Wizard automatic
32. 6 Inertial Explorer Chapte ri 1 5 5 Loading IMU Solutions This feature loads of the project s IMU solution files Choosing to load the forward IMU solution file FIM or the reverse solution file RIM loads the solutions most recently processed in the respective direction The combined IMU solution file CIM only exists if you have combined your FIM and RIM files Loading Smoothed IMU Solutions This feature is virtually identical to that described above but it loads the most recently smoothed IMU trajectory files The files available for loading depend on the directions in which smoothing has been performed See Chapter 4 3 6 on Page 70 for help using the RTS smoother Input Formats The boresighting module supports input from external data files so ensure compatibility before attempting to use any of these files The list of fields supported for input is provided under the File formats drop down menu of the given import window All fields must be space delimited and appear in the same order as that specified by the File format selection made under the drop down menu If there are column headers in the input file they are skipped Ensure that the proper units are specified under the Attitude units drop down menu The IDs used in the input file must match those used in Inertial Explorer in order for the boresighting module to correctly relate corresponding data Any XYZ coordinates imported for the
33. 8 20 Manual for information regarding all of the features available via this menu Only those features exclusive to Inertial Explorer are discussed here 1 7 1 Plot Results Refer to Chapter 2 of the GrafNav GrafNet Version 8 20 Manual for information regarding all of the GNSS plots available here Table 1 in the shaded box on this page and the following page contains a description of the IMU plots available only through Inertial Explorer 44 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 1 7 2 Export Wizard Only the Export Wizard window exclusive to Inertial Explorer is discussed here Refer to the GrafNav GrafNet Version 8 20 Manual for additional information concerning this feature IMU Epoch Settings Epoch Output Interval The Kalman GPS interval indicates the interval used during GPS processing while the IMU integration interval displays the interval at which the IMU data was processed These values can only be changed prior to processing The Output data interval defines the interval to export solutions The output interval can be set as high as 1000 Hz regardless of what interval the data was processed at The time range for which to obtain outputs can also be limited here Lever Arm Offset Allows for the coordinates of the IMU calculated via the IMU Kalman filter to be transferred to an alternate sensor s location The orientation of t
34. BTF BTR BTC IMU Binary File SBTF SBTR dela SBIF SBIR SBIC Sere IMU Message Log FIL RIL FTL RTL IMU Smoother FB RBI FBT RBT Binary File 4 11 2 How do I engage loosely coupled and or tightly coupled processing in Inertial Explorer Both methods of processing are available in Inertial Explorer Loosely coupled processing is performed in two stages First the GNSS data is processed to produce a trajectory This can be done through differential processing by using Process Process GNSS or through precise point processing by using Process Process PPP Regardless of which method is used ensure that you have achieved satisfactory results before moving on The next stage is to engage the IMU processor by going to Process Process IMU It is important to double check that the combined solution file whether it be the CMB file from differential processing or the CSP file from precise point processing is used as the source for position updates This can be verified under the Forward and Reverse tabs under the Source of GNSS Updates box Tightly coupled processing is performed in one step by going to Process Process TC The window that appears gives you access to all of the same GNSS and IMU processing options that are available during loosely coupled processing Once you have configured them click on the Process button to engage tightly coupled processing lt Both styles of processing can be pe
35. ENSING OR PRODUCTS OR SERVICES IN NO EVENT SHALL NOVATEL BE LIABLE FOR SPECIAL INDIRECT INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND OR NATURE DUE TO ANY CAUSE Inertial Explorer 8 20 User Guide Rev 6 15 Software License 16 Inertial Explorer 8 20 User Guide Rev 6 Terms and Conditions 1 PRICES All prices are Firm Fixed Price EX WORKS 1120 68th Avenue N E Calgary Alberta All prices include standard commercial packing for domestic shipment All transportation insurance special packing costs and expenses and all Federal provincial and local excise duties sales and other similar taxes are the responsibility of the Purchaser 2 PAYMENT Terms are prepayment unless otherwise agreed in writing Interest shall be charged on overdue accounts at the rate of 18 per annum 1 5 per month from due date To expedite payment by wire transfer to NovAtel Inc Bank HSBC Bank of Canada 407 8 Avenue S W US Account 788889 002 Calgary AB Canada T2P 1E5 Transit 10029 016 Swift HKBCCATTCAL DELIVERY Purchaser shall supply shipping instructions with each order Ship to and bill to address NovAtel Quotation Preferred carrier and account Custom broker freight forwarder including name and contact In the absence of specific instructions NovAtel may select a carrier and insure Products in transit and charge Purchaser accordingly NovAtel shall not be responsible for any failure to perform due to unforeseen
36. Explorer s cycle slip detection using only the receiver s locktime to determine measurement validity Although this option can improve accuracies in some extreme conditions it is generally not recommended Enable Heading Updates from File Certain applications benefit greatly from the use of external heading updates Examples of these applications include where a low quality IMU is used or where it is impossible to follow recommended alignment procedures or where a vehicle moves very slowly and or does not experience many changes in heading External heading updates are obtained by first processing the relative vector between two antennas mounted on the same vehicle as the IMU For best results knowledge of the accuracy of the heading update as well as the constant offset between the IMU and the two GNSS antenna must be known The HMR data format is described in Section 3 2 2 on Page 56 Inertial Explorer 8 20 User Guide Rev 6 31 Chapter 1 Inertial Explorer IMU Processing Settings 2 xd Reverse GNSS Advanced Error Model User Cmds System General Forward DMI Mount W Browse Info r Settings DMI observation treatment DMI measurements treaded as velocities I Automatically detect ZUPTs from DMI sensor Measurement standard deviations Velocity 0 20000 m s Wheel circumference NoVeluel m IV Use value from file header Cancel Apply DMI To in
37. GNSS derived information to update the IMU Kalman filter Specifically the IMU processor reads in the positions velocities and their corresponding variances as output during GNSS processing The IMU processor reads this information and uses it to update the positions which would otherwise drift due to the nature of inertial systems It follows from this that loosely coupled processing is two step system Because the GNSS data is used to compute positions and or velocities at least four satellites are needed Tightly coupled processing on the other hand entails the use of GNSS and IMU data in one Kalman filter The primary advantage is that the filter can be updated using as little as two satellite measurements making it the preferred method of processing when poor GNSS conditions are encountered The IMU data is also used to help detect reject poor GNSS measurements while the phase information can still be used to aid KAR in resolving ambiguities Inertial Explorer 8 20 User Guide Rev 6 81 Chapter 4 FAQ and Tips Table 4 Inertial Explorer Extensions for File Type GNSS Solution Output Files Loosely Coupled FWD REV CMB or Tightly Coupled FWD REV CMB FSP RSP CSP GNSS Static Se FSS RSS FSS RSS PG Message EML RML FML RML IMU Solution FIM RIM CIM FTM RTM CTM IMU Solution SFTM SRTM dr SFIM SRIM SCIM SLIM IMU Binary File BIF BIR BIC
38. MU processing the values displayed reflect those calculated in the IMU Kalman filter using the GNSS information as updates Ideally these values should agree When they do not monitor the position and velocity misclosure 1 11 Help Menu 1 11 1 Help Topics Opens an HTML version of this manual with the GrafNav portion included This feature is a quick and easily accessible reference 1 11 2 The Waypoint Products Group s Web Page This option opens a web browser to the Waypoint Products Group s page on NovAtel s website where details on the latest versions patches information on GNSS INS and technical reports can be found 46 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 1 11 3 About Inertial Explorer This window displays information about the software version build dates copyright information hardware lock key information and DLL information Access the hardware key utility from this window by clicking Key Util Upgrade This tool is useful for upgrades The Dependent Files window displays a list of executables and DLLs associated with Inertial Explorer The date and time of the files are shown as well as a quick description of the file Click Download latest manufacturer files to connect to Waypoint s FTP site Internet connection required to download the files listed in the shaded box Most of these manufact files have an associated user file where personal inform
39. NSS data help In general we believe from our experience that I Hz GNSS data is sufficient even for updating MEMS IMUs This is a decision that you can make from your own experience with their specific application We suggest that you process at 10 Hz and then I Hz and make your own judgement Clearly processing time is saved if you can justify the lower update rate 4 10 4 What should I look for while the IMU data is processing Examining the Processing Inertial Display Box is a useful exercise while the data is processing Keep an eye on the GNSS IMU Misclosure relative to the velocity This relates to the difference in the GNSS update coordinates and the coordinates computed by the IMU while the IMU was running in stand alone mode since the last update If you know what the relative misclosure values should look like during a good mission you will have an idea while the data is processing whether outliers exist in the data set Advanced users can also view the gyro and accel biases for unexpected large offsets as the data is being run Speed or velocity is also a good value to monitor In a worst case scenario an unusual large speed is a good first indicator of trouble 80 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 4 11 Tightly Coupled Processing Tips 4 11 1 Whatis the difference between loosely coupled and tightly coupled processing Loosely coupled processing refers to the usage of
40. NovAtel Inc All rights reserved Unpublished rights reserved under L 9 International copyright laws Printed in Canada on recycled paper Recyclable 2 Inertial Explorer 8 20 User Guide Rev 6 Table of Contents Ee EE 9 Software License miennenenanneanananananaenaananaannnnaaananaanareaaanaaaaanannnanaaaaaaaanannnnanaanaaaanannae 13 Warranty EE 15 Terms and Conditi ONS cecssecscveezcedecttevesheceecthanessnpseaceadeaverden duh katad avada valvavad t ank koa avaga nad 17 1 Inertial Explorer 19 1 1 Overview of Inertial Explorer 19 1 2 Getting Started with Inertial Explorer 19 1 3 File MENU EE 22 T T NEw ET 22 1 3 2 Add Master File S none a nll a a it i eae vie 22 1 3 3 Add Remote File 554725 redan med ard header kalte EEN kak ka 22 1 3 4Add HA IEN EE 23 1 3 5 GONVOr nsavmsni ide ahta kamide kalana daa add ahta eddik aada aaa daa a ad a d e 23 13 6 Removing Processing ME 28 14 View Men enoro auti taa kahar aadi dal adra aaia ka amaan katva leitu da a 24 1 5 tee 24 1 5 1 Process IMU loosely coupled n vvnnnnnanennnnaaananaannnanaanaaaaannnanaananaanannae 24 1 5 2 Process TC tightly Coupled IMU nuvsnnenennnaaananaenananana anna nannaaaaanaaa annan 38 1 5 3 Combine and Gmoofb A 39 1 5 4 Solve Boresighting Angles isnennennenananneeennnaaaaanaanannenaaananaannnaaaanaaaanaaeee 40 1 5 5 Loading IMU Solut
41. Scale Ze Data is delta theta Data is angular rate Accelerometer Measurements Inverse Accelerometer Scale Factor fi 000000 00000000 1 Accel Scale Ze Data is delta velocity C Data is acceleration r Timing Settings Data Rate 100 0 Hz GPS IMU time tag bias offset fo 0000 s Byte Order Intel C Motorola GPS seconds of week C UTC seconds of week r Time Tag Format Time Tag Source C GPS Received Time GPS Corrected Time Cancel 2 1 2 Creating Modifying a Conversion Profile New Creates a customized profile to convert unique format into Waypoint s generic IMR format This is used for custom scale factors data rates and orientations in raw data files Modify Allows changes to be made to an existing profile Delete Deletes an existing profile Rename Renames an existing profile Sensor Timing Settings Gyro Measurements Pertains to the measurements made by the gyroscopes The inverse value of the scale factor is required For example a scale factor of 0 0004 which can be represented fractionally by 1 2500 should be entered as 2500 The gyro measurements can take the form of delta theta where angular increments are being observed or angular rate Accelerometers Measurements Considerations similar to those made for the scale factor of the gyro measurements should be made here That is to say the inverse of the sca
42. TE Fil Siini e an Slee deta ENEE EN 59 3 3 2 FIM RIM FTM RTM Files MM u ssseeeeeeereeer reen ter enker renerne ener 60 Inertial Explorer 8 20 User Guide Rev 6 3 Table of Contents 3 3 3 BIF BIR BTF BTR Files hindre ees vedama koa aada Sa 61 4 FAQ and Tips 63 4 1 Overview of FAQ and pe 63 4 2 How are Inertial Explorer and coordinate frames related u u u sseeeerereen nerne rn nn nrnee 63 4 2 1 What is an inertial frame successen 63 4 2 2Whatis a computation fram CN 64 4 2 3 What is a navigation frame u ssseeseeeeee ennen 64 4 24 Whatis a eet 64 4 3 What should I know about inertial processing numrenenneneonnaanannnnananaaaananane na 65 4 3 1 Why are error models so Important seneste nen 67 4 3 2 Why is alignment so important ernreneonnvnnorrrrnnnnnnnnrrrrnnnnnnnnrrrrnnnnnrnnnenrrennnnnnnrenrensnnnnnnennenn 68 4 3 3 What s staticalignment uvaner bh talla krae kuta ka aata 68 4 3 4 What is kinematic alignment u u u ssseeee ennen renerne 69 4 3 5 What is IMU Kalman filtering a sscccieesseassgetecssadtegescdasanceneate ENEE Aknad dekaan vaada 69 4 3 6 What is Kalman filter smoothing tnnmnenenneneannaanannenananaanananennananaaaaanaa anna 70 4 4 What do I need to know about Boresighting nnrsnanreennenaanaanannnnanananananannn eat 71 4 4 1 Why is boresighting needed mnrnnrnnrnnannnvnnnnrrennnnnvnnrr
43. This system provides coordinates in terms of East North and Up or if preferred in latitude longitude and height Attitude information is presented in terms of roll pitch and yaw which reflect the vehicle s heading The origin of this system is defined as the centre of the sensor array The Z axis is orthogonal to the reference ellipsoid at the sensor array while the Y axis points North and the X axis points East What is a navigation frame When making computations in the Local Level frame instabilities can arise near the poles due to convergence of the meridians lt This is not a problem in the case of Inertial Explorer because it performs its calculations in the ECEF frame instead 4 2 4 What is a body frame This frame is aligned with respect to the vehicle s body In this discussion it is assumed that the accelerometer and gyro measurements are made in the body frame of the vehicle This called a strapdown approach to inertial navigation The orientation of a vehicle s body frame is completely arbitrary from one epoch to the next One of the principal challenges in any inertial survey is to properly compute the orientation of the b frame with respect to a chosen computation frame at each and every measurement epoch For instance body to I frame angles are roll pitch and yaw 64 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 The B frame chosen for Inertial Explorer is d
44. a system tied to the stars does not move for the duration of a typical survey 1 Dr El Sheimy University of Calgary 63 Inertial Explorer 8 20 User Guide Rev 6 Chapter 4 FAQ and Tips Figure 3 Body Frame Definition XY The body frame definition of the measurement unit may very likely be different from that shown above simple reflection of your body axes into the body axes given by Inertial Explorer is typically all that is required to process data 4 2 2 What is a computation frame The frame in which Inertial Explorer performs its GNSS and inertial computations is the Earth Centred Earth Fixed ECEF frame The origin of this system is located at the centre of mass of the Earth a point which is well defined by observing the orbits of satellites together with gravity measurements The Z axis is coincident with the spin axis of the Earth and is therefore co incident with the Z axis of the I frame The X axis of the ECEF system points through the Greenwich Meridian while the Y axis completes a right hand orthogonal frame The ECEF frame differs from an inertial earth centred frame only by the amount the earth rotates 4 2 3 The purpose of a navigation frame is to allow the ease visualization of the navigation of the vehicle Inertial Explorer employs the Local Level frame because it is an appropriate reference system in which coordinates and attitude information can be output in an intuitive manner
45. agree Use Build Custom List to add some of the these plots to the list Export Final Coordinates The steps for exporting final coordinates are in the shaded box Plot Results Select Plot X Axis Aus List of variables CTRL click to select multiples E SS EH E E E Most Common ks Accuracy Measurement far Separation beg Quality Control ke Coordinate Values beg Attitude bes IMU ke Miscellaneous Pas All Add Group Edit Build Custom How to export final coordinates 1 Select Output Export Wizard 2 Specify the source for the solution Epochs outputs the trajectory while Features Stations exports positions only for loaded features such as camera marks 3 Select a profile For Inertial Explorer select IMU Data as the profile 4 Click Next 5 Use the processing datum for the datum screen lt If prompted for the geoid undulation file it can be found on the distribution CD Inertial Explorer 8 20 User Guide Rev 6 21 Chapter 1 Inertial Explorer Project Wizard Steps 1 Create and name the project 2 Add rover data to the project The rover data can be in Waypoint s GPB format or in the receiver s raw format in which case the Wizard converts it to GPB for you If you are a NovAtel SPAN user and you add a raw data file the Wizard automatically detects the IMU model
46. alignment assuming any is present Roll and pitch are estimated from the sensed gravity components in the horizontal axes of the accelerometer triad while yaw is estimated from the sensed Earth rate about the leveled gyro axes Typically while even MEMS sensors can make some estimation of roll and pitch the Earth rate is often masked by noise for lower grade IMUs The values entered here for x and y which represent pitch and roll are often as much as an order of magnitude smaller than that for z which represents yaw If in doubt simply enter large values in the range of thousand of arc seconds and allow the IMU Kalman filter time to eventually compute more sensible estimates of the error in the computation of the attitude matrix These values must be entered in degrees Accel Bias These values represent the initial uncertainties in the a priori knowledge of the constant bias errors in the accelerometer triad They are in relation to the accelerometer biases entered under the Advanced tab If these bias values were left at zero meaning that they are unknown then the standard deviation values entered here should reflect this uncertainty The processor then computes the biases on the fly These values should be entered in m s 36 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Gyro Drift These values refer to the initial uncertainty regarding the a priori knowledge of the sensor drift in th
47. ally detects the user s raw data types converts them to GPB and if requested downloads nearby service station data The IMU model is automatically detected for NovAtel SPAN users Other new features include the following New file handling routines effectively remove file size limitations for raw data up to 7 days RTS Smoother now smoothes attitude as well as position e For marine applications a new Heave option is available to apply heave compensation Support for auto stabilized camera mounts added External heading updates can now be used e New plots for raw IMU gyroscope and accelerometer measurements Lever arm values can now be read into software if present in IMR header Improvements e IMU settings have been re organized in a more intuitive fashion e Processing profiles can now be easily loaded through the IMU settings e New residual tests help ensure better filtering of position phase and ZUPT updates e Maximum number of allowable external coordinate updates CUPTs has been increased to 1 000 e Decreased memory consumption means that smoothing IMU data is now faster Bug Fixes Bug fixed in DMI Residual plot where computed DMI velocities were being plotted instead of the residuals Bug fixed in kinematic alignment where an error was returned if the GPS data was greater than 1Hz e High rate data outputted through Export Wizard no longer contains position jumps at top of the second Bug fixed in File Data Covera
48. amined to insure the software was run with correct input parameters especially Error Model and that the data itself was not contaminated with outliers either within the raw IMU output or from the update coordinates or velocities 4 12 1 How is the IMU quality Q number different from the GNSS Q number Actually the Q number displayed after the IMU finishes processing is a combination of both the previously stored GNSS Q number and the currently computed Q number relative to the IMU processing The IMU Q number takes into account the filtered misalignment estimates and variances as well as the position misclosure estimates and position variances The GNSS Q values is then meaned with the IMU Q number The IMU Q number is weighted towards medium accuracy IMUs It is an empirical value and will probably tend towards 6 red for a low quality MEMs IMU For this reason among others the Waypoint Group always suggests to analyze more than the Q number Plots to examine after IMU processing Attitude Separation Plot The forward reverse attitude separation after alignment period reflects about 2 times the actual error in roll pitch and heading This statement is empirical but has been taken from experiments where truth data has been available so far as we can obtain truth data Right click on the plot display and put in a start end plot time which eliminates the alignment period and perhaps the
49. ation is saved These files are not modified when you download the latest manufacturer files It is important for this reason to not modify the manufact files as they are overwritten when this option is used Manufacturer files available to download from Waypoint s FTP site manufact adf List of antenna profiles Refer to the GrafNav GrafNet Version 8 20 Manual for more details manufact dn1 List of base stations available for the Download utility This is usually updated monthly manufact dtm List of datums ellipsoids and transformations between datums Refer to Chapter 11 of the GrafNav GrafNet Version 8 20 Manual for details manufact fvt List of Favourites and the groups they are contained in These only contain coordinates for stations available with the Download utility Refer to the GrafNav GrafNet Version 8 20 Manual for more information manufact grd List that contains available grids such as UTM US State Plane Gauss Kruger etc Refer to the GrafNav GrafNet Version 8 20 Manual for more details manufact svi A file that associates a PRN number with a satellite type Block II Block IIA etc for purposes of determining the center of mass of the satellite It assists in single point processing This file should not be modified manufact cim Provides a set of default conversion parameters for various IMU raw data formats This file is accessed during the conversion from raw data to IMR format See Cha
50. ay need to be reduced by an order of magnitude Position Position spectral densities are noise densities that account for unmodeled position effects during each Kalman prediction Apply all of the considerations mentioned above here for the velocity spectral densities User Commands Certain options available in Inertial Explorer cannot be accessed through the options menu A full list of configured options is available under this tab and may be invoked to employ special features or overwrite defaults For an explanation of all the commands available here see Appendix A on Page 85 1 5 2 Process TC tightly coupled IMU This window provides access to most settings related to tightly coupled IMU processing See Section 4 11 on Page 81 for more information and refer to the GrafNav GrafNet Version 8 20 Manual for information regarding all of the features available via this menu Only those features that are exclusive to Inertial Explorer are discussed here Settings Gives the option of the processing direction GNSS Settings See Section 1 5 on Page 24 for more information IMU Settings See Section 1 5 on Page 24 for more information 38 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 1 5 3 Combine and Smooth Refer to the GrafNav GrafNet Version 8 20 Manual for Function to Perform Smooth and Combine i xl information regarding th tions Onl int Combine forward and re
51. begin processing automatically activate the Start processing right away box The Auto Start steps are in the shaded box 1 3 2 Add Master File s Entering the proper reference station coordinates is essential for obtaining high accuracies The values that appear are averaged from the GPB file and may have errors of 10 metres or more For IGS and CORS stations ARP antenna reference point coordinates are pre loaded in the Favourites Manager Refer to Chapter 2 of the GrafNav GrafNet 8 20 Manual for more information Proper datum selection is very important as well CORS sites are stored in NAD83 and IGS sites in WGS84 WGS84 coordinates are different from NAD83 coordinates by 2 m so care should be taken when using these coordinates BY Be sure to set the ellipsoidal orthometric height 3 Choose the Remote File It must contain GNSS data collected during the same time period as the reference station 4 Choose a Processing Profile that best suits the application When in doubt choose either the Factory Defaults or GrafNav Defaults Continued in the shaded box on the next page flag correctly 1 3 3 Add Remote File When the adding the remote GNSS data file enter the remote station antenna height If it is not entered then the final height coordinates includes the antenna height and this causes a vertical shift If only the ellipsoidal or orthometric height of the antenna is of interest then enter zero
52. c data in the Kalman filter process to fine tune the initial roll pitch and yaw computations If GNSS updates are immediately available following coarse alignment many applications can choose to fine tune the attitude information from the GNSS information available during navigation For instance an airplane that taxies down a runway may have sufficient time and update information to adequately perform a dynamic fine alignment By the time the aircraft reaches the area where the mission takes place the attitude matrix and associated sensor biases may be optimized as well as possible without static fine alignment For low grade IMUs the GNSS update process can also provide some approximation of heading during navigation This works best in minimal crab environments 4 3 4 What is kinematic alignment It is also possible to transfer initial roll pitch and yaw from another sensor while in kinematic mode Moving coarse alignments are even possible from only GNSS update information Be aware that the process of alignment is similar to the convergence process which must be undertaken for computation of GNSS integer phase ambiguities Unless using a very expensive IMU do not expect to obtain optimal values for attitude until some static and kinematic data collection has taken place This is in the order of minutes not seconds Analogous to GNSS kinematic IMU alignments take longer than static alignments The first 5 to 10
53. d WAY P3HINT PRODUCTS GROUP A NovAtel Precise Positioning Product Inertial Explorer OM 20000106 Rev 6 Inertial Explorer User Guide Publication Number OM 20000106 Revision Level 6 Revision Date 2009 04 30 This manual reflects Inertial Explorer software version 8 20 Proprietary Notice Information in this document is subject to change without notice and does not represent a commitment on the part of NovAtel Inc The software described in this document is furnished under a licence agreement or non disclosure agreement The software may be used or copied only in accordance with the terms of the agreement It is against the law to copy the software on any medium except as specifically allowed in the license or non disclosure agreement No part of this manual may be reproduced or transmitted in any form or by any means electronic or mechanical including photocopying and recording for any purpose without the express written permission of a duly authorized representative of NovAtel Inc The information contained within this manual is believed to be true and correct at the time of publication NovAtel Waypoint Inertial Explorer GrafNav GrafNet GPSolution ProPak OEMV OEM4 and RT 2 are registered trademarks of NovAtel Inc SPAN DL 4plus ProPak G2plus ProPak LBplus PAC Ad Vance and RT 20 are trademarks of NovAtel Inc All other product or brand names are trademarks of their respective holders ZA O Copyright 2009
54. deally the magnitude of these plots agree with the manufacturers specs on drift and bias lt Some of the judgements made on the quality of the graphs described above will come from the experience It is difficult to provide absolute numbers at this point as IMUs differ by orders of magnitude depending on their manufacture Inertial Explorer 8 20 User Guide Rev 6 77 Chapter 4 FAQ and Tips 4 9 How can I use the alignment of the IMU It is important to choose a start and end time to begin IMU processing for both forward and reverse procedures IMUs need to obtain initial values for the integration of gyro rate measurements to rotations and accelerations to coordinate differences The alignment period allows you to compute initial approximates for roll pitch and yaw Initial coordinates may be entered or simply read from the GNSS processed data files Ideally you need STATIC data for the alignment procedure at both the beginning and end of the GNSS INS mission 4 9 1 How much static alignment data do I need In general for GNSS INS processing you only need 1 2 minutes of static coarse alignment data at the beginning and end of each data set In a non ideal situation Inertial Explorer can handle as little as 4 seconds of static data for coarse alignment Fine Alignment is an option but not really a requirement if good GNSS data is available when the vehicle starts to move 49 2 How do I find start end t
55. e IMU to vehicle deg Rot 0 0000 yRot rg 2Rot 0 0000 Z m Zero Velocity Updates ZUPTS Name Starts 0 00000e 000 P Add Edt Remove Load 30 0 D Add Edt Remove Load m Heave Compensation for Height IV Apply Heave Window seconds Cancel Apply IMU Processing Settings GNSS Advanced User Cmds Reverse Error Model System General Forward DMI Mount m Error Model Select error model vi m Initial Standard Deviation Values Misalignment 1 1111e002 heit 277784000 deg 2 0000e 004 3 0000e 004 3 0000e 004 metres s 2 27780005 Een En degs r Spectral Densities Values square root of Misalignment 2 7778e 004 2 7778e 004 27785004 deg s Accel Bias 3 1623e 006 8 1623e 006 beem metres s 2 Gyro Drift 8 7841e 010 8 7841e 010 8 7841e 010 deg s Velocity fr 0000e 003 fr o000e 003 fr 0000e 003 m s Foo kaocn ac m Accel Bias Gyro Drift Position Ux Ux Inertial Explorer 8 20 User Guide Rev 6 35 Chapter 1 Inertial Explorer IMU Processing Settings 21x System General Forward Reverse GNSS Advanced Error Model DMI Mount Error Model Select error model User Cmds Iv Initial Standard Deviation Values Misalignment frittieoo2 frittieoo 27778e 000 deg Accel Bias 3 0000e 004 3 0000e 004 3 0
56. e boresight rotation as clockwise from north TE will use the yaw definition by negating this so we have a right hand definition that fits with internal computations double dBoreSightRotationZStdDev Approximate accuracy of the boresight angle in degrees If not known set it zero char Extra 212 Reserved for future use bytes should be zeroed heading_hdr_type The single header which is a total of 256 bytes is followed by the following 24 byte structure type for each measurement record typedef struct double dGpsTime GPS seconds of the week short sGpsWeek GPS week number use 1 if not known double dHeading Input heading update in decimal degrees definition is positive rotation clockwise from north Note that IE uses yaw i e rotation counterclockwise from north Yaw heading float fHeadingStdDev Standard deviation of the update in decimal degrees zero if not known enter approximation using input dialog or CFG file command heading_rec_type 58 Inertial Explorer 8 20 User Guide Rev 6 Data and File Formats Chapter 3 3 3 Output Files This section discusses the different output files that are created when processing with Inertial Explorer 3 3 1 FIL RIL FTL RTL Files Message Log files echo all error and warning messages sent to the Process Window during INS processing Some example messages are in the shaded box FIL RIL FTL RTL message files
57. e gyroscopes Again if the biases under the Advanced tab were left at zero then enter standard deviations values here that reflect this The program attempts to compute reasonable values during processing All values should be entered in degrees sec Spectral Densities Values Generally speaking the lower the grade of the sensor the larger the spectral densities that should be used for processing s previously discussed the spectral densities add noise to the covariance propagation process prior to filtering Therefore the higher the densities the greater the weight that is placed on the GNSS updates during filtering The following mathematical quantities are available Misalignment A misalignment noise density in arcseconds2 sec becomes a covariance when multiplied by some time interval dt If the sensor triad is problematic in terms of providing an accurate attitude matrix or if initial alignment is poor then you may need to introduce large spectral density values here These spectral components add noise to the computed Kalman covariances for misalignment which in turn forces the processor to rely more heavily on the GNSS position and velocity updates As a result large errors in the direction cosine matrix are compensated for Accel Bias Accelerometer bias densities when multiplied by the prediction time interval act as additive noise to the accelerometer bias states As such larger values here may help to com
58. e roll pitch and heading values along with their associated standard deviations is displayed for each loaded camera event The coordinates of the IMU at the time of the event is also displayed These values are generally transferred from Inertial Explorer directly and correspond to the IMU values interpolated at camera event times Photo E O values The omega phi and kappa values along with their associated standard deviations are displayed for each loaded camera event These values are produced externally in a photogrammetric package Matches residuals Before the computations begin choose whether or not to include the observations associated with a camera event in the least squares procedure by simply right clicking on the event Once the least squares procedure has finished the window is updated with the final residual values at each camera event Additional information such as quality indicators and computed omega phi and kappa values are also displayed Time Range This setting controls which period of time to perform the combining and or smoothing of the trajectories Epochs outside of this time range is not considered and does not appear in the output files Combine Any Two Solutions This option combines any two trajectory files whether they be derived from GNSS only or GNSS IMU processing It provides a means of comparing the trajectory obtained before and after smoothing 1 5 4 Solve Boresighting Angles P
59. e system In some cases IMU processing cannot be performed at all without a properly chosen error model Error Model The options available are to the use one of the error models provided or use a custom model The former option entails selecting one of the models from the scrolling window each of which has a set of initial standard deviation and spectral density values associated with it These models have been optimized for the indicated application or sensor through the processing of multiple sets of applicable data Because all values have been empirically derived through a trial and error process the accuracy achievable by their use cannot be guaranteed Certain profiles have been tailored for certain conditions as opposed to specific sensors For example the Navigation High Precision model is most suitable for high end units with gyro drift rates on the order of 0 01 hr or better whereas the Tactical Medium Precision model is aimed at medium grade systems with drift rates in the range of 1 hr to 10 hr The Automotive Low Precision model allows the Kalman filter to loosen up in order to compensate for poor field conditions such as short or non existent static alignment DMI Mount EmorMode UserCmds System General Forward Reverse GNSS Advanced Initial Gyro Drift Values gt I Manual value entry J7 Manual value entry m s 2 deg s m Sensor gt Body Rotation r Initial Accel Biases Rotat
60. ed read the messages to ensure the expected number of camera events have been read in Once the calibration procedure is complete the final boresighting values as well as the number of iterations needed to arrive at them are displayed The following options are available via the buttons along the bottom of the Solve Boresight Angles window Compute Assuming all the required input data has been loaded press this button to begin the iterative least squares procedure The Message Window contains pertinent information regarding the success or failure of the procedure Settings This button gives access to the Boresight Settings window which is useful for configuring many parameters used in the boresight calibration Axes System Definition The options are listed in the shaded box Grid Map Definition The options made available here depend on the system definition chosen above If the input angle were provided with respect to a map grid then the selection made here determines the convergence value a used to form the R matrix In addition grid users are given the opportunity to enter the average ground height in order to maximize accuracy Measurement Weighting The selections made here determine the composition of the variance covariance matrix used in the least squares procedure to derive the final boresighting values Choose to enter a set of constant standard deviation values to apply to all measurements or have t
61. ed attitude accuracy plots for sudden relative movements in the plot These are indications of point problems in the survey Remember that these plots are derived from a covariance analysis and do not take into account system bias and process noise These error sources have to be implied from the plots of forward reverse separation position misclosure and so on Gyro Drifts and Accel Biases Please load the forward and reverse solutions separately and then plot these values Inertial Explorer 8 20 User Guide Rev 6 83 Chapter 4 FAQ and Tips 4 12 2 What plots should I examine after IMU Processing There are particular plots to bring up each time you process an IMU data set including the ones listed in the shaded box on on Page 83 Simply put these plots following alignment should appear to be more or less horizontal lines across the page They should also appear to have a magnitude roughly in line with the manufacturers specification Again if Error Models are of interest these plots are critical in that development Otherwise if inconsistent with specs they may simply be showing the effects of a survey in a poor environment 4 12 3 How do I smooth and export data The final step in the process is to smooth the forward or reverse or combined solution and then export the results through Export Wizard A few things to remember here include e Make sure the lever arm values have been fixed not re computed e I
62. eiver status event warnings Factory Defaults Cancel AGI1 AG58 AG17 AG62 53 Inertial Explorer 8 20 User Guide Rev 6 Chapter 3 Data and File Formats 3 2 File Formats 3 2 1 IMR File Waypoint converts all custom IMU raw binary formats into a generic format IMR which is read from Inertial Explorer following the decoding process in IMU Data Converter See Chapter 2 on Page 49 for more details Because it contains vital information for reading and decoding the data the first 512 bytes of the generic IMU data format is a header which must be filled in read and interpreted In a C C structure definition the generic format header has the following fields struct imr_header_type char szHeader 8 char blisintelOrMotorola double dVersionNumber int bDeltaTheta int bDeltaVelocity double dDataRateHz double dGyroScaleFactor double dAccelScaleFactor int iUtcOrGpsTime SIMURA W 0 NULL terminated ASCII string 0 Intel Little Endian default I Motorola Big Endian swap bytes for IExplorer This can be set for any user who directly writes in our format with a Big Endian processor IExplorer will swap the bytes Program version number i e 8 20 Default is 1 which indicates the data to follow will be delta thetas meaning angular increments i e scale and divide by by dDataRateHz to get degrees second Ift
63. el revolution Must be set if logging accumulated tick count or ticks second char cExtra2 420 Reserved for future use bytes should be zeroed The single header which is a total of 512 bytes is followed by one of the following structure types for each DMI measurement record struct dmi_lrec_type If logging using LONG values EN SSync Sync byte Set to Oxffee short sWeek GPS week number set to 1 if not known double dTime GPS time of week in seconds unsigned long IValue DMI NUM DIM values counts DMI NUM DIM should be equal to sDim k struct dmi drec type If logging using DOUBLE precision ei SSync Sync byte Set to Oxffee short sWeek GPS week number set to 1 if not known double dTime GPS time of week in seconds double dValue DMI NUM DIM A values double precision DMI NUM DIM should be equal to sDim Inertial Explorer 8 20 User Guide Rev 6 57 Chapter 3 Data and File Formats 3 2 3 HMR File Users wishing to include external heading updates during inertial processing must first convert their data into Waypoint s generic format HMR NOTE Data structures must be packed on a 1 byte boundary typedef struct char szTitleStr 20 SIMUHEADING to identify this as a heading update file double dVersion Program version number double dBoreSightRotationZ Heading boresight rotation about Z clockwise in degrees zero if not known use positiv
64. ent for the use directly indirectly by implication or otherwise by Licensee of the name of NovAtel or of any trade names or nomenclature used by NovAtel or any other words or combinations of words proprietary to NovAtel in connection with this Agreement without the prior written consent of NovAtel 3 Patent Infringement NovAtel shall not be liable to indemnify the Licensee against any loss sustained by it as the result of any claim made or action brought by any third party for infringement of any letters patent registered design or like instrument of privilege by reason of the use or application of the Software by the Licensee or any other information supplied or to be supplied to the Licensee pursuant to the terms of this Agreement NovAtel shall not be bound to take legal proceedings against any third party in respect of any infringement of letters patent registered design or like instrument of privilege which may now or at any future time be owned by it However should NovAtel elect to take such legal proceedings at NovAtel s request Licensee shall co operate reasonably with NovAtel in all legal actions concerning this license of the Software under this Agreement taken against any third party by NovAtel to protect its rights in the Software NovAtel shall bear all reasonable costs and expenses incurred by Licensee in the course of co operating with NovAtel in such legal action 4 Restrictions You may not a use the software on more t
65. epicted in Figure 3 The Y axis of the body frame is co incident with the longitudinal axis of the vehicle Its positive direction points out the nose of the vehicle The Y axis may also be said to define the roll axis of the vehicle where positive roll being counter clockwise in a right hand system The positive X axis of the B frame points out the right side of the vehicle when one is standing in the vehicle and facing the positive Y direction It contains the vehicle pitch rate The positive Z axis of the body frame points up through the roof of the vehicle A yaw rate is said to be positive if it is measured counter clockwise about the Z axis 4 3 What should I know about inertial processing To process measurements made in an inertial frame the body frame needs to be re oriented in such a way as to make it coincident with the computation frame or eventually the navigation frame if they are different In other words body frame measurements should be sensed directly in the desired computation frame Furthermore only those components which are due to motion of the vehicle are of interest Hence gravity Earth rotation and the curved shape of the Earth as sensed by the gyroscopes and accelerometers must be eliminated to ensure that any sensed accelerations come only from vehicle dynamics For example in the computation frame if accelerations along the north pointing axis are integrated twice there is a direct difference in
66. eration in the body s Y axis The approximate roll and pitch values computed from these measurements be used to define an approximately level plane Initial heading still needs to be computed and this is where inexpensive IMU sensors tend to suffer Gravity provides a strong signal and it can be sensed adequately by even MEMS grade accelerometers Heading or yaw must be computed by examining the output of the gyroscopes for Earth rate For instance for an ideal stable platform system the assumption is that one horizontal axis points due East A gyroscope aligned along this axis is in a no torque situation relative to the Earth rotation Hence there is no output On the other hand the North pointing axis senses the entire Earth rate at that latitude Consider the magnitude of the Earth rotation rate at about 15 hour MEMS rotation sensors can have drifts in the order of 100 hour to 300 hour and the you can see that the computation of heading during coarse alignment with such sensors is impossible In fact any output from such a gyroscope during static alignment can be simply considered to be noise meaning that it can be modeled as a bias Systems drifting at about 1 hour should be able to gyrocompass to some degree of accuracy Systems above this may require external aiding for azimuth determination 68 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 Fine alignment is the process of using stati
67. ero Velocity Updates ZUPTS D gt al Edt Remove Load Add Edt Remove Load D m Heave Compensation for Height IV Apply Heave 2 0 Window seconds Cancel Apply Ux Inertial Explorer does not rely on the presence of this information so if these values are not known then leave them as zero In such instances the calibration of the sensor is attempted through the alignment procedure and the ensuing GNSS updates throughout the mission Zero Velocity Updates Inertial Explorer takes advantage of periods when the IMU is static Such periods of time are referred to as zero velocity updates ZUPT Upon reaching the start of a ZUPT Inertial Explorer assumes the data to be static and replaces the GNSS velocity update values with zeros Inertial Explorer automatically detects the presence of ZUPTs by analyzing the GNSS IMU and if available DMI data This is true for both loosely and tightly coupled processing As such the manual entry of ZUPTs is generally not necessary except in cases of poor data quality Consult the IMU Status Flag plot after processing to determine the periods where a ZUPT was detected Ifa known ZUPT was missed manually enter it here Coordinate Updates This option is only available for performing IMU processing without the aid of GNSS data Otherwise this functionality must be carried out automatically via GNSS updates throughout the missio
68. f outdated ephemerides For NovAtel OEMV BESTPOS trajectory can be exported to a GrafNav compatible format For Trimble DAT better handling of station names and more than 12 satellites In GPB2RIN command line version is now available and some bug fixes have been implemented Inertial Explorer 8 20 User Guide Rev 6 11 Inertial Explorer Version 8 00 The major new addition for Version 8 00 is Tightly Coupled TC processing It uses GPS carrier phase to limit error where satellite tracking is limited or variable even if only 2 or 3 satellites are visible Another important enhancement is the addition of a new API to permit much expanded automated processing The new API now provides complete feedback and permits calling application to better control processing progress Other improvements include 12 Non integer data rates now fully supported Improved processing and back smoothing of low or variable data rate inertial data Better support in back smoother and IMU processing for data SPANning the GPS week crossover Binary output from processing engine can now be written at a lower data rate than processing interval Local time can now be exported for hour time zones Text names of time zones can be specified X and Y axes ranges from one data plot can be transferred to others Better display of larger IMU time gaps in File Data Coverage Plot Ability to utilize real time position such as OmniSTAR SBAS RTK from BESTGPS posit
69. f the IMU processing settings where a number of error models appropriate to specific classes of IMUs are available for selection You can also build custom error models suitable to particular inertial measurement units or applications Unlike GNSS inertial computations are very sensitive to the input a priori stochastic information that is available for each inertial system As a rule of thumb the more expensive the IMU the less likelihood of achieving poor results from a non optimal choice of input statistical quantities A poor choice of noise densities for a navigation grade inertial system may simply provide a sub optimal set of outputs for attitude An inappropriate choice of noise densities for a MEMS array with a drift of 300 hour may mean that nonsense is obtained for attitude information The process of choosing an appropriate variances and spectral densities for a particular system is referred to as tuning Unfortunately tuning often tends be a somewhat arbitrary process You might have to simply guess at the approximate magnitude of the noise densities which help describe the behavior of an inexpensive inertial system This can be a tedious and occasionally unrewarding process The creation and tuning of error models for various classes of IMUs is an on going task at NovAtel s Waypoint Products Group The latest error models are included in a file called manufact imu which can be found in the software installation directory Waypoint P
70. fectly aligned No matter how perfect the mechanical installation is there will most likely be small angular errors that persist between the systems For an object in the image this error can be quite significant when projected onto the ground For the case of a frame imager this angular difference can easily be solved for using photogrammetric means 4 42 How does the boresighting module work The module that comes with Inertial Explorer uses a simple boresighting procedure that utilizes the omega phi and kappa angles computed by some external bundle adjustment package It then computes the differences between them and internally generated values from the IMU processing 4 4 3 What are omega phi and kappa Omega phi and kappa are Euler angles that represent the angular difference between the imaging and the ground coordinate systems The differences between roll pitch and yaw ve heading and omega phi and kappa are explained in Table 3 on Page 70 in the shaded box Inertial Explorer 8 20 User Guide Rev 6 71 Chapter 4 FAQ and Tips What you need to get started with the module A data set flown over a targeted calibration field with 4 flight lines in opposing directions e g north south east and west and 4 to 6 photos in each line Imagery must have 60 overlap along each line stereo photography is highly desirable and a minimum of 20 side lap between lines e The imagery must have tie
71. first and last few minutes of trajectory determination Look at the fwd rev separation in the attitudes and decide whether your error is acceptable or within tolerances In a data set with no other known issues this plot also reflects the fit of the Error Model to the IMU that you are using Advanced users may use this to modify or build their own custom Error Model Position Misclosure Plot You should obtain an idea of the expected misclosure between the IMU coordinates and the GNSS update coordinates at each update point for their own IMU For example several centimeters over a 1 sec interval is expected for a tactical grade IMU Consistently and unexpectedly large position misclosures are good evidence of problems with the IMU survey and vice versa Combined Separation Plot This plot shows the coordinates differences between the forward and reverse IMU process This plot should also be reflective of the GPS combined separation It is not exactly the same but should be in the same region error wise A common problem is a sub metre or decimeter level difference between forward and reverse This may be due to a lever arm problem Make sure you fix your lever arms at some value before outputting your final coordinates Otherwise your forward reverse separation floats along with the filtered value of the lever arm states This will bias the coordinates you deliver to your client Estimated Attitude Accuracy Look at the estimat
72. from manufact imu or user imu Scale GPS Kalman co variances for positions and velocities by this amount ON OFF Use GPS heading updates constant offset deg standard deviation of offset angle deg Lever arm in meters measured in body frame GPS INS UPDATE TOL FLOAT FIXED sdev Q D rms GPS POSITION UPDATES ON OFF GPS TRAJECTORY SOURCE source GPS VELOCITY UPDATES ON OFF Inertial Explorer 8 20 User Guide Rev 6 Only use GPS updates if standard deviation quality factor and Doppler RMS are below tolerances Enable disable GPS position updates Set GPS solution file 0 CMB 1 FWD 2 REV 3 external file Enable disable GPS velocity updates 85 Appendix A Appendix A GPS UPDT INT n GPS updates every n seconds FIXED FLOAT ambiguities def FLOAT std dev GPS _ coord def i 2m Q factor 1 6 def 6 DopplerRms m s GRAFNAV_FILE filename filename2 Name of trajectory source file for GPS updates forward and reverse GYRO BIASES x yz X Y Z gyro drifts in deg sec GYRO NOISE sd1 sd2 sd3 Spectral density of the gyro drift states in arcsec sec GYRO SD xsdev ysdev zsdev A priori Kalman standar deviations for X Y Z gyro drift states in arcsec sec INITIAL ATTITUDE KNOWN att ATTITUDE KNOWN HEADING KNOWN ATTITUDE UNKNOWN Refers to validity of the initial roll pitch yaw values INITIAL_ATTITUDES rowfwd pitchfwd azfwd rowrev pitchrev azrev If known input initial roll pitch
73. from the ground system to the image or IMU system Only the omega primary phi secondary and kappa tertiary rotation order is supported Axes Use this to define the orientation of the image system The most commonly used system is the conventional frame where the x axis points forward the y axis points left and the z axis points upwards The frame defined here determines the composition of the R matrix Inertial Explorer 8 20 User Guide Rev 6 41 Chapter 1 Inertial Explorer Solve Boresight Angles BETA xl Show Navigation values DI Angles in degrees SD Resid and BS in ArcMin Roll Pitch Heading RolsD PitchSD Head 2 Settings Calibration name BS View report after computation B S Angles deg r Auto update navigation angles on entry 16 11 46 Boresight module version 8 00 0613 16 11 46 c Copyright NovAtel Inc 2007 16 11 46 IV Add results to list use for Export Close Settings New Load gt View gt Clear Moa Display Units These options pertain to the values displayed in the Solve Boresight Angle window and determine which units are used when writing to the Boresight Report file These options also allow the number of decimals places to which all values are displayed or written to be modified New This button clears any stored data from previous calibration runs in order to start a new one Load Use this to load the required navigation and exterior or
74. g data using DOUBLE precision Measurement type distance or speed I if logging a distance measurement 2 if logging a speed measurement Number of DMI sensors Maximum is 3 but only 1 can be used in Inertial Explorer Measurement resolution of DMI 1 if low resolution i e only makes measurements on the full wheel revolution 3 if high resolution i e makes measurements at partials of a wheel revolution or on fixed time intervals Type of distance measurement Must be set if sMeasType distance measurements 1 if logging accumulated tick count 2 if logging distance in meters 3 if logging accumulated distance in meters Type of velocity measurement Must be set if sMeasType 2 velocity measurements 1 if logging velocity in meters second 2 if logging velocity in ticks second Scale factor m count or m s count Must be set if sValueType is set to 0 1 0 if logging accumulated tick count or ticks seconds If logging in meters or meters second then dScale will scale measurements into corresponding units 56 Inertial Explorer 8 20 User Guide Rev 6 Data and File Formats Chapter 3 char szAxisName DMI MAX DIMJ 16 Name of various axes DMI optional NULL terminated double dWheelSize Size of the wheel in meters Must be set if logging accumulated tick count or ticks second long ITicksPerRevolution Number of tick counts per whe
75. ge plot where gaps in GPS data where not being plotted once an IMR file had been loadedNeed content Inertial Explorer Version 8 10 Version 8 10 uses NovAtel s Advance RTK ARTK on the fly OTF engine that fixes carrier phase ambiguities faster and at longer distance than GrafNav s KAR algorithm ARTK also has fewer failed fixes than KAR and produces a lower separation between forward and reverse trajectories PPP processing accuracy has been improved by up to 40 by refining the solution with an additional processing pass and by applying higher order corrections For high altitude or long distance data sets much of the tropospheric error can be removed by the addition of a Kalman filter bias state Such methods have often had problems in differential mode and we have solved this problem by using GrafNav s PPP processor to compute the tropospheric bias trajectory for each base station This tool can also be used to check the base station coordinates In multi base mode base stations can be rejected if the base remote distance is longer than a user set tolerance Satellites with low C NO can be rejected from the filter 10 Inertial Explorer 8 20 User Guide Rev 6 Version 8 10 also includes an improvement on automated Zero Velocity Update ZUPT detection User interface improvements The map window and plot windows can be zoomed in and out with the mouse wheel and maps can be displayed with a white background and can be copied t
76. han one computer simultaneously with exception of the Windows and WinCE data logging software which may be copied and used for each GPS receiver collected data simultaneously b distribute transfer rent lease lend sell or sublicense all or any portion of the Software without the written permission of NovAtel c alter break or modify the hardware protection key dongle thus disabling the software copy protection d modify or prepare derivative works of the Software e use the Software in connection with computer based services business or publicly display visual output of the Software f implement DLLs and libraries in a manner that permits automated internet based post processing contact NovAtel for special pricing g transmit the Software over a network by telephone or electronically using any means except when downloading a purchased upgrade from the NovAtel web site or h reverse engineer decompile or disassemble the Software Inertial Explorer 8 20 User Guide Rev 6 13 Software License You agree to keep confidential and use your best efforts to prevent and protect the contents of the Software from unauthorized disclosure or use 5 Term and Termination This Agreement and the rights and licences hereby granted shall continue in force in perpetuity unless terminated by NovAtel or Licensee in accordance herewith In the event that the Licensee shall at any time during the term of this Agreement 1 be in breach
77. he flag is set to 0 then the data will be read directly as scaled angular rates Default is 1 which indicates the data to follow will be delta v s meaning velocity increments i e scale and divide by dDataRateHz to get m s If the flag is set to 0 then the data will be read directly as scaled accelerations i e 100 0 records second If you do not know it set this to zero and then fill it in from the interface dialog boxes Scale multiply the gyro measurements by this to get degrees sec if bDeltaTheta 0 Scale the gyros by this to get degrees if bDeltaTheta 1 If you do not know it then the data can not be processed Our default is to store the gyro data in 0 01 arcsec increments or 0 01 arcsec sec so that GYRO SCALE 360000 Scale multiply the accel measurements by this to get m s if bDeltaVelocity 0 Scale the accels by this to get m s if bDeltaVelocity 1 If you do not know it the data can not be processed Our default is to store the accel data in le 6 m s increments or le 6 m s so that ACCEL SCALE 1000000 Defines the time tags as being in UTC or GPS seconds of the week 0 Unknown default is GPS 1 UTC 2 GPS 54 Inertial Explorer 8 20 User Guide Rev 6 Data and File Formats Chapter 3 int iRcvTimeOrCorrTime double dTimeTagBias char szimuName 32 bool bDirValid unsigned char ucX unsigned char ucY unsigned char
78. he frame in which these coordinates must be entered You are also free to save your offset for future use via the Favorites button 1 8 Tools Menu Refer to Chapter 2 of the GrafNav GrafNet Version 8 20 Manual for information regarding all of the options available via this menu Table 1 IMU Plots con t Plot Description IMU Status Shows the status of IMU processing Specifically Fla this plot provides indication of the type of update if 9 any being applied at each epoch This plots presents the body frame components of the lever arm offset between the IMU and GNSS IMU GPS antenna If the offset was manually entered then Lever Arm this plot bears constant horizontal lines If left to be solved by the Kalman filter this plot shows the computed values Leaded This plot is the difference between the IMU heading COG g and the GNSS course over ground values Effects difference of crabbing shows up as a direct bias in this plot Plots the difference between the East North and Velocity Up components of velocity computed during Separation forward and reverse processing Requires that both directions be processed and combined This plot shows the difference between the GNSS solution and the mechanized INS positions IMU GPS obtained from the GNSS INS processing This is a Position good analysis tool used to check the GNSS INS Misclosure solution as well as checking INS stability Large jumps or spikes
79. he values derived from either the navigation SD values the photo SD values if provided or a combination of both The other setting here pertains to the outlier tolerance The value specified here determines at which point a measurement is removed from the least squares procedure Boresight Settings xj Axes System Definition System SEET EE 29 deg order TXTYTZ Order w primary P secondary K tertiary fandt zl T 0 0 deg MU Sensor Ares forward Y left Z up conventional fran Y Tz 00 deg r Grid Map Definition Datum WwGS84 UTM Zone 15 i henge Average ground height 1044 4 m Display Units Attitude values Degrees v nDecimals 4 SD residual and boresight values nDecimals 2 r Measurement Weighting SD source Use constant values below ES OmegaSD 0 0167 deg PhisD 0 0167 deg KappaSD fo 0500 deg Outlier detection tolerance 3 0 NSD Factory Defaults Are Minutes Y Axes System Definition options System The selection made here defines the ground coordinate system to which the omega phi and kappa values are oriented see Section 4 4 on Page 71 for a description and diagram of the navigation values Normally they are referenced to a map projection which is defined in the Grid Map Definition settings Order This setting defines the order in which the omega phi and kappa angles are to be applied during the transformation
80. ht be good to 10 cm or so After obtaining the best lever arms possible you can run the smoother and output your coordinate and attitude values DO NOT SOLVE the lever arms on the final processing run Fix them as you obtained them Otherwise the final coordinates vary as the lever arms vary 4 8 How important is error model tuning Choosing a correct Error Model for the type of IMU utilized is critical The Kalman filter can not and will not operate effectively unless the A priori Error Model agrees with the specifications given for the initial standard deviations and especially the spectral noise densities for the given type of gyros and accelerometers Even within IMU types for example 1 degree hour tactical grade systems Error Models can differ and must be optimized to provide expected performance Additionally Error Models are not guaranteed to be optimal for missions outside normal dynamic ranges Examples include rocket tests or race car dynamics Typical dynamics include van surveys or airborne photogrammetric surveys In general the Error Models supplied should not have to be modified by the typical user for their dynamic environment The Error Models are stored in ASCII profiles There are also Error Models supplied by the Waypoint Group See the file called MANUFACT IMU This file should not be modified Instead add your own profiles to the user file 76 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips
81. ientation input data The navigation data can be obtained either by loading the latest set of roll pitch and heading values computed by Inertial Explorer or by an external file which contains this information for each camera event Alternatively if such information is available there is the ability to provide the module directly with the omega phi and kappa angles required to rotate the ground system into the IMU frame Obtaining the attitude angles directly from Inertial Explorer is by far the most common usage The exterior orientation parameters for each photo must be supplied by an external file This file should contain the omega phi and kappa angles required to rotate the ground system into the image system View This button gives access to the post calibration report The report contains relevant boresight calibration information as well as a list of all the input data provided for each camera event The bottom of the report displays the boresight values and residuals from the final iteration This report can be viewed through either NotePad or the internal Inertial Explorer ASCII viewer This button also gives you access to the calibration history For each calibration run the final boresighting results have been saved assuming the Add results to list option is enabled Clear Msg This button simply clears the Message Window of any messages currently displayed 42 Inertial Explorer 8 20 User Guide Rev
82. imes for the IMU alignment Prior to GNSS processing under the Plot tool select File Data Coverage This plot shows the overlapping data between GNSS base GNSS rover and IMU data files This plot provides you with an idea of when to possibly start and end the IMU processing The following two questions may remain 1 Are the start and end times in a static period 2 How long do these static periods last If the GNSS data has been processed load the GNSS forward reverse or combined solution and plot the GNSS derived velocity Again the times are on the X axis of the plot This Velocity plot can be used in conjunction with the File Data Coverage plot to provide a good A priori idea of start end time for alignment and the number of seconds of alignment in both forward and reverse directions 78 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 4 9 3 How can I use kinematic alignment If no static alignment data is available or you must re align due to a inertial data gap then alignment while moving is possible and under good conditions can produce acceptable results It is important to examine the velocity plot if possible to choose a section of the vehicle motion which is straight and level All that is required is 4 seconds of straight level flight or motion for kinematic alignment to achieve its purpose If the section of data chosen does not work choose another section until the desired result
83. ion record from SPAN in inertial processor Events from SPAN MARKTIME2 can be exported to a separate file permitting support for dual event marks CUPTs and ZUPTs can now be loaded from a file Inertial Explorer 8 20 User Guide Rev 6 Software License BY INSTALLING COPYING OR OTHERWISE USING THE SOFTWARE PRODUCT YOU AGREE TO BE BOUND BY THE TERMS OF THIS AGREEMENT IF YOU DO NOT AGREE WITH THESE TERMS OF USE DO NOT INSTALL COPY OR USE THIS ELECTRONIC PRODUCT SOFTWARE FIRMWARE SCRIPT FILES OR OTHER ELECTRONIC PRODUCT WHETHER EMBEDDED IN THE HARDWARE ON A CD OR AVAILABLE ON THE COMPANY WEB SITE hereinafter referred to as Software 1 License NovAtel Inc NovAtel grants you a non exclusive non transferable license not a sale to use the software subject to the limitations below You agree not to use the Software for any purpose other than the due exercise of the rights and licences hereby agreed to be granted to you 2 Copyright NovAtel owns or has the right to sublicense all copyright trade secret patent and other proprietary rights in the Software and the Software is protected by national copyright laws international treaty provisions and all other applicable national laws You must treat the Software like any other copyrighted material and the Software may only be used on one computer at a time You may not copy the product manual or written materials accompanying the Software No right is conveyed by this Agreem
84. ions AANEREN 43 1 6 Settings Menu maaange eee eee ei kaa 44 1 61 IMU une EE 44 1 7 OUTPUT Mengen EE Ee deeg cde aa aa ats Mane ewe 44 1 71 ed 0 p 50 OE EE EE 44 172 Export Wizard viii 15011408 ects Pd et a ed nn es Pd te 45 1 8 TODIS METU i artet dnadmin eet ieee ee ee 45 1 9 Interactive WindoWS x si stuatesvatttatvi kihk dvd je NE he duties kb nedb na Aat A 46 1 10 Processing WINKOW AH 46 LITH dE TEE 46 1 44 41 Help tele LTE 46 1 11 2 The Waypoint Products Groups Web Page steenanneeannnennannenananananana 46 1 11 3 About Inertial Expl rer miscmmmrern iuitsumiiisnibtem item na Tahkuna eehaaccenepedacedeeveddaeaeeess 47 2 Conversion Utilities 49 2 1 Raw IMU Data Converters eu iiss ised cet ateees detiiie di aaa settee EES a a aa 49 2 1 1 Waypoint IMU Data Conversion erne renerne renerne 49 2 1 2 Creating Modifying a Conversion Profile vsmrenennennnananannneenannannannnnane 50 2 1 3 Sensor Orientation Settings rsrnnrennnnnaenenneenaanannannenananaanannnnenannaanananneana 51 21 4 Decoder Settings um risinn aa Tade ia a uk eee AAMU ka 51 3 Data and File Formats 53 3 1 Data Formals iio scceecavecehpeiaid detent a ab AIEA SIE Edge EES ege re eae aka aa 53 3 1 1 NovAtel s SPAN Technology 53 3 2 File Formats ged gedreet seen marenandreassen 54 KC RUE 54 3 22 DMR ET 56 9 2 9 HMR KEE 58 9 9 Output UE 59 33 1 FIL RILFTLR
85. is employed the R is computed by Equation 4 in the box The quantity R corrects for the map convergence and is computed by Equation 5 in the box Where difference between grid north and true north see convergence angle in Section 1 7 2 on Page 45 imu The final quantity required to solve for PK ig TT which represents the rotation required to orientate the IMU into the ground coordinate system and is computed by Equation 6 in the box It is also useful to present the matrix required to rotate a ground coordinate system into an alternate coordinate system This matrix is defined through Equation 7 in the box Equation 1 X X p g o RL YY f Z Z 8 0 Where x y image coordinates Xp Yp principal point offset f focal length k scale factor Xg Ve Zg ground coordinates Xo Yo Zo perspective centre coordinates Equation 2 Roge AR ppe Re Equation 3 Rim R RR Equation 4 R R _ 0 6 0 7 2 0 0 Eguation 5 cosa sina 0 R sing cosa 0 0 0 1 Equation 6 cos ycosr sin ysin psinr sinycosp cos ysinr sin ysin pcosr R sin ycosr cosysinpsinr cosycosp sin ysinr cos ysin pcosr cos psinr sin p cos pcosr Where r roll angle p pitch angle y yaw angle yaw heading Equation 7 cos cosk Rope cos sink cos cosK sin sing cos sink sin sin COSK sin sin x cos sin COSK sin singsink sin cosk cosa sin sin x
86. know if my error model is working There are three main tests to determine if an Error Model is optimized for a given IMU or even for a special dynamic environment After processing a reasonable data set without too much bad data or any bad data plot the list in the shaded box from the Plot Menu Plots to test if an Error Model is optimized for a given IMU 1 IMU GNSS position misclosure This value represents the difference in the stand alone IMU solution since the last GNSS update against the current GNSS solution If the GNSS coordinates are good the error plotted is due to the performance of the inertial mechanization equations over the last n seconds Clearly if you have metres of error over one second then you have a poorly determined Error Model 2 Forward Reverse Attitude Separation Plot This is the most important graph to examine in the course of model determination Experience has shown that the forward reverse attitude separation when optimized is roughly twice the reasonable expected error from your system So if a spectral density is changed and the attitude separation worsens you know that you have gone in the wrong direction and so on 3 Gyro Drift and Accel Bias Plots First load the forward or reverse but not combined IMU solution Simply put the gyro drift and accel biases should appear to be horizontal lines more or less across the plot They should look like biases not ramps or random noise I
87. le containing the GPS time as well as the gyroscope and acceleration measurements of all three axes for the first thousand epochs Use this to detect any errors that may occur during the conversion such as the use of an incorrect scale factor Path Displays the path to the directory containing the input file All output files created by this utility are saved to the directory IMU Profiles Displays a scroll down list of profiles available for use during conversion Each profile contains a set of conversion parameters designed to decode measurement data files produced by the indicated sensor Choose one profile from the list or if necessary create one See Section 2 1 1 on Page 49 for help Once all the appropriate fields have been entered click the Convert button to start converting IMU data into IMR format A message window appears to show the status of the conversion process 49 d waypoint IMU Data Conversion xl Input Output Files Input Binary IMU File FEER Browse Output Waypoint Binary File Output Waypoint ASCII File For viewing the data first 1000 epochs I Output ASCII Path IMU Profiles El Rename New Copy Delete About Convert im Modify e Inertial Explorer 8 20 User Guide Rev 6 Chapter 2 Conversion Utilities Sensor Timing Settings Sensor Orientation Decoder Settings r Gyro Measurements Inverse Gyro Scale Factor 1 Gyro
88. le factor is required Much like the gyro measurements the accelerometer measurements can take two forms the first being data velocity or velocity increments and the other being acceleration Timing Settings Enter the data collection rate of the IMU sensor here and specify any offset that may exist between the GNSS and the IMU time tags Byte Order This flag must be properly set If the proper byte order is not specified the decoding of the binary raw file will fail 50 Inertial Explorer 8 20 User Guide Rev 6 Conversion Utilities Chapter 2 Time Tag Format There are only two options available here as the data is either acquired in the GPS time frame or the UTC time frame This must be correctly identified in order for the IMU data to be properly aligned with the GNSS data Time Tag Source Specify here whether the time tags represent the GPS Corrected Time or the GPS Received Time 2 1 3 Sensor Orientation Settings Defined the orientation of the IMU here using the steps in the shaded box The orientation will always be right handed 2 1 4 Decoder Settings Specifies which library will be used to perform the conversion based on the input format of the raw data file For most sensors this should be left untouched For SPAN the IMU decoding is handled through the GNSS decoder Sensor Timing Settings Sensor Orientation Decoder Settings m Man
89. lease see Section 4 4 on Page 71 for a description and diagram of the navigation values Show This drop down menu is linked to the window below it and gives viewing access to the values listed in the shaded box Settings The following features are available Calibration name Enter a name to distinguish calibration runs from one another Inertial Explorer keeps a history of calibration runs so a unique identifier is helpful when trying to recover previous results This is useful for using multiple systems and or tracking stability over time Boresight Angles Upon successful completion of the calibration procedure the final values for the computed boresight angles are displayed here Add results to list When this option is enabled the last values computed by the program are stored so that they are easily accessible by the Export Wizard View report after computation Enabling this option forces the software to launch the boresighting report upon successful completion of a calibration The contents of the report are discussed later on Auto update navigation angles on entry When this option is enabled Inertial Explorer loads the latest navigation values for the camera events into the boresighting module 40 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Message Window This window provides valuable insight on the status of the current calibration Whenever input data is being load
90. me used here is mission dependent and should be chosen with care because a poor alignment results in poor attitude and coordinate information End Time Same considerations as above This time determines the point at which forward processing stops and when reverse processing begins Interval Data Rate Settings The following settings are available IMU raw data rate This is the number of IMU epochs second collected and time tagged in the binary IMU measurement file This value should be double checked The integration interval for IMU processing is the inverse of this value Extract from IMR header For uncertain IMU data rates enable this option to allow the software to read it in from the header in the IMR file This option assumes that the proper conversion parameters were used to create the IMR file GNSS update interval This value specifies the rate that Inertial Explorer performs GNSS updates Updates cannot be performed at a rate higher than the GNSS data processing Performing updates at a rate higher than 1 Hz is not helpful unless the data was collected in an environment with high dynamics 26 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Use every GNSS epoch This option forces the processor to use every xd computed epoch outputted during GNSS DMI Mount ErorMode UserCmds System General Forward Reverse GNSS Advanced processing It sets the update i
91. minutes of fine alignment Within 5 to 10 minutes GNSS updates enable the IMU to provide attitude information consistent with the accuracy level achievable by the accelerometer gyro triad with or without fine alignment This depends on the type of IMU and the application s requirements After roll pitch and yaw are roughly estimated for coarse alignment fine alignment refines them to a better level of precision 28 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Transfer alignment If roll pitch and yaw are known these values can be entered as initial integration constants to allow navigation to proceed Attitude angles can be provided by another IMU in which case the misalignment between the IMUs must be applied or they can be extracted from another trajectory such as the opposite processing direction Click Enter Attitude to scan the first epoch appearing in the IMU trajectory file of the direction opposite that of the one being processed The attitude and velocities as well as their standard deviations are loaded Kinematic alignment When neither static data or a priori attitude information are available alignment can be done using vehicle motion This requires a short period of time where the vehicle is relatively level and moving in a relatively straight line followed by some higher dynamics such as an aircraft S turn The time period can range from 4 to 40 seconds depending
92. misalignment states in arc seconds NUM STATES number Number of Kalman filter states Inertial Explorer 8 20 User Guide Rev 6 86 Appendix A POSITION MEAS VAR cov POSITION NOISE sd1 sd2 sd3 POSITION SD esdev nsdev usdev PREDICTION RATE n TIME OFFSET offset TOTAL ALIGNMENT TIME timel time2 VEL MEAS VAR var VELOCITY NOISE sd1 sd2 sd3 VELOCITY SD sdev1 sdev2 sdev3 WRITE BINARY OUTREC ON OFF ZUPT ALIGN INTERVAL interv ZUPT AT name start end ZUPT OPTION num ZUPT TIME time ZUPT VEL TOL tol Inertial Explorer 8 20 User Guide Rev 6 Appendix A Variance R matrix of Kalman CUPT observation in m Spectral density of the coordinate states in m s A priori Kalman standard deviations for E N U coordinate states in metres Kalman filter predictions every n seconds Default is 0 5 Correction in seconds to GPS times in the IMU binary file Default is zero Seconds of coarse fine alignment Note that no fine alignment is performed when total align time coarse align time Variance R matrix of Kalman ZUPT observation in m s Spectral density of the velocity states in m ei A priori Kalman standard deviations for E N U velocity states in metres sec Write binary structure to disk at mechanization rate for FWD REV combination Length of time for a ZUPT during fine alignment Name start time GPS sec and end time GPS sec of ZUPT 0 one epoch or 1 best fit
93. n Without the presence of GNSS data the positions being computed from the inertial data are likely to drift drastically over time This option bounds these errors by allowing the processor to correct its trajectory at any given time where the position is known This requires that the IMU have traveled over a previously surveyed point and that you know the exact time at which this occurred Since it is unlikely that the IMU was physically placed upon this point the lever arm offset must also be entered 34 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Apply Heave For marine users who wish to apply heave compensation to the computed ellipsoidal height use this option to utilize Inertial Explorer s low pass filter The algorithm requires that a window size reflecting the period of the wave motion be entered The value computed with this option replaces the ellipsoidal height All trajectory files output files and plots where ellipsoidal heights are outputted with this option will now show the new heave compensated height values Error Model Options This is one of the most important components of processing IMU data successfully In general the less expensive the sensor package the more tuning that is required to find initial variances and spectral densities that work optimally for that particular IMU For some MEMS sensors it is critical that spectral densities match the sensor noise of th
94. n the Smooth and Combine dialog box make sure Smooth both directions and combine is selected BISee Section 1 5 3 on Page 39 for help using the smoother The final ASCII format output through the Export Wizard is user configurable if you do not find our IMU profiles suitable 84 Inertial Explorer 8 20 User Guide Rev 6 Appendix A Summary of Commands ACCEL BIASES xyz ACCEL NOISE sd1 sd2 sd3 ACCEL SD xyz ALIGNMENT MODE mode ASCII OUTPUT INTERVAL Interval COARSE ALIGNMENT MODE mode COARSE ALIGNMENT TIME timel time2 CORRELATION TIMES gyro time accel time DATA RATE rate DYNAMICS MODE mode GPS COVARIANCE SCALE pos vel GPS HEADING UPDATES OFF ON const StdDev GPS INS OFFSETS dx dy dz Accelerometer biases in m sec Spectral densities of the accelerometer bias states in m s A priori Kalman standard deviations for accelerometer bias states in m s O coarse fine align 1 coarse align only 2 no alignment transfer or on the fly alignment ASCII IMU output to FIM RIM files Default is 1Hz O static coarse alignment 1 Jenter the az 2 transfer alignment Seconds of coarse alignment for FWD REV processing Correlation time for Gauss Markov gyroscope and accelerometer bias states in seconds Data rate for IMU 64 Hz for LTN90 50 Hz for LRF3 50 Hz for LN200 100 Hz for HG1700 IO How 1 high 2 Jextreme ERROR MODEL IMU Name Error model name
95. navigation frame is a function of three consecutive rotations in yaw pitch and roll The implemented computation frame is ECEF so the attitude matrix must be further rotated as function of latitude and longitude Changes in orientation 1 e angular rates must be integrated once in order to obtain angles This implies two things the first being that it is a requirement to solve for three initial constants for the integration process to be complete Secondly as with the accelerometers errors are integrated along with the measurements The integration process can then quickly accumulate errors from the gyroscopes 66 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 GPS antenna IMU gt GPS offset vector T IMU gt Camera offset vector Angular misalignment AR grid map projection coordinate system y grid north 4 ME Local level system y true north d Notes 0 4 referenced to grid coordinate system ground to air roll pitch yaw referenced to local level coordinate system air to ground AR expressed in w d system Figure 4 IMU Camera 4 3 1 Why are error models so important Error models are more important for inertial processing than GNSS processing The term error model in the context of Inertial Explorer refers to the initial variances and a priori spectral noise densities required by the IMU Kalman filter These values are provided via the Error Model tab o
96. ndirect or consequential damage whatsoever that may be suffered by the Buyer In the event and to the extent that NovAtel shall have any liability to Buyer pursuant to the terms of the Order NovAtel shall be liable to Buyer only for those damages which have been foreseen or might have reasonably been foreseen on the date of effectivity of the Order and which are solely an immediate and direct result of any act or omission of NovAtel in performing the work or any portion thereof under the Order and which are not in the aggregate in excess of ten 10 percent of the total Order price Inertial Explorer 8 20 User Guide Rev 6 Chapter 1 Inertial Explorer 1 1 Overview of Inertial Explorer Waypoint Products Group s Inertial Explorer post processing software suite integrates rate data from six degrees of freedom IMU sensor arrays with GNSS information processed with an integrated GNSS post processor same as GrafNav s Inertial Explorer utilizes strapdown accelerometer Av and angular rate A0 information to produce high rate coordinate and attitude information from a wide variety of IMUs Inertial Explorer implements either a loose coupling of the GNSS and inertial data or tightly coupled TC processing that uses GPS carrier phase to limit error during periods where satellite tracking is limited or variable even if only 2 or 3 satellites are visible It is important to time tag the inertial measurements to the GPS time frame during
97. ned by the laws of the Province of Alberta Canada Each of the parties hereto irrevocably attorns to the jurisdiction of the courts of the Province of Alberta 10 Customer Support For Software UPDATES and UPGRADES and regular customer support contact the NovAtel GPS Hotline at 1 800 NOVATEL U S or Canada only or 403 295 4900 Fax 403 295 4901 e mail to wpsupport novatel ca website http www novatel com or write to NovAtel Inc Waypoint Products Group 1120 68 Avenue NE Calgary Alberta Canada T2E 8S5 14 Inertial Explorer 8 20 User Guide Rev 6 Warranty NovAtel Inc warrants that during the warranty period a its products will be free from defects and conform to NovAtel specifications and b the software will be free from error which materially affect performance subject to the conditions set forth below for the following periods of time Computer Discs Ninety 90 Days from date of sale Software Warranty One 1 Year from date of sale Date of sale shall mean the date of the invoice to the original customer for the product Purchaser s exclusive remedy for a claim under this warranty shall be limited to the repair or replacement at NovAtel s option and at NovAtel s facility of defective or nonconforming materials parts or components or in the case of software provision of a software revision for implementation by the Buyer All material returned under warranty shall be returned to NovAtel prepaid by the
98. ngs This option is only available for combining unfiltered forward and reverse files Enabling this option creates a BIC BTC file which contains the inertial trajectory at the mechanization rate Use this option for exporting either the camera events or high data rate epochs Smoother Settings The following options are only available for performing RTS smoothing Direction s to smooth RTS smoothing can be performed in just one direction or both Much like GNSS and GNSS IMU processing it is recommended that smoothing be performed in both directions Output files Use this to change the filename and filepath of the output files created during smoothing Be aware that name changs removes the file s automatic association to the project Chapter 3 on Page 53 provides a description of the file formats Inertial Explorer 8 20 User Guide Rev 6 39 Chapter 1 Inertial Explorer x Show Navigation values v Angles in degrees SD Resid and BS in ArcMin Pitch Heading RollsD PitchSD HeadSD Latitude E IV Add results to list use for Export I View report after computation T Update navigation angles on entry Settings s TT ve 9 15 53 Boresight module version 8 10 2130 9 15 53 c Copyright NovAtel Inc 2008 9 15 53 Calibration name B S Angles Settings New Load gt View gt Clear Msg Close Values that are visible with the Show drop down menu Navigation values Th
99. nn Cup Cve Cvn Cvup TraceCpos m m s Att Roll Pitch Azimuth RollSD PitchSD AzimuthSD All values in meters Drf GyroX GyroY GyroZ GX sd GY sd GZ sd All values in degrees sec Bia AccelX AccelY AccelZ AX sd AY sd AZ sd All values in m s Ecf ECEF XECEF YECEF Z All values in meters Kal MisalignX MisalignY MisalignZ dX dY dZ dVx dVy dVz Arcsec m m s Mis GPS IMU e GPS IMU n GPS IMU u GPS IMU vn GPS IMU vn GPS IMU vu GPS IMU position velocity misclosures Acc AccelEast AccelNorth AccelUp Accelerations in m s Ang RollRate PitchRate YawRate Angular rates in degrees sec Fli C A N U 1 2 3 7 C oarseAlign Fine A lign N avigation U pdate 1 AlignMode 2 VelocityUpdate 3 GPSUpdate 4 CoordinateUpdate 6 Predicted 7 Interpolated Flg S K NsGps NsGin F L lonoMode S D S tatic KJinematic number of GPS sats number of GLONASS sats F ixed F L oat 0 Off 1 IonoFree 2 RelativeModel SJingle D ual Sta GPS IMU_QualityNum GPS_amb_drift GPS_dd_dop pdop hdop vdop 1 6 cycles sec DOPs Rms L1 phase ca range pi range L1_doppler RMS from GPS m m m m s A numerical example is also given Out Tim 242454 000 242454 000000 1326 Geo 38 58 32 81833 90 01 56 81759 447 3102 0 000 Loc 27954 263 25107 254 419 862 37 048 64 995 1 432 Var 4 45898e 004 7 89335e 004 1 63980e 003 1 97879e 004 2 37932e 004 2 62523e 004 2 87503e 003 Att 21 4595 2 8034 203 8579 1 05545e 002 1 12253e 002 2 25285e 002 Drf 5 10860e
100. northing from some known starting location Similarly differences in easting and height can be obtained by integrating twice along the other two accelerometer axes provided these are properly oriented If the initial coordinates at the centre of the sensor array are known at the start of a mission the coordinate differences can be used to compute latitude longitude and height for every epoch in the trajectory Inertial Explorer 8 20 User Guide Rev 6 65 Chapter 4 FAQ and Tips The problem lies in the fact that sensor biases measurement noise errors in initial conditions and gravity modeling errors are all integrated along with the measurements In terms of attitude the single integration results in the platform becoming misaligned with the computational system In terms of position this misalignment causes the gravity vector to enter horizontal axes while the double integration of these errors leads to an additional quadratic error The end result is that significant errors can be quickly realized The rotation matrix required to take body sensed measurements and place them in the computation frame at any given epoch is referred to here as the attitude matrix The gyro triad is utilized to sense the change in vehicle rotation from the body frame orientation at one epoch to the subsequent body frame orientation at the next epoch The direction cosine matrix which is defined in Inertial Explorer to go from body frame to
101. nterval equal to that SE File Info used for GNSS processing IMU file E DatatinertalExploreriIMUNSPAN AG58 ar Info ASCII Kalman output MIMU Time Range This field determines the rate at which the epochs ee EE are written to the ASCII solution files Use these Begintime 164254 00 Endtime 168820 00 ASCII files for plotting and inspection Sn I Process IMU data only Use GNSS update interval i S A IV Output binary values for smoother Enabling this option is recommended especially A A A Interval Data Rate Sett if there is not an interest in reading the ASCII dee solution files These files are written at epochs IMU raw data rate where a GNSS update was performed If an GNSS update intervat 1 000 5 JT Use every GNSS epoch update is not available mechanized values output ASCII Kalman output 1955 fs use GNSS update interval at the top of the second Binary high res output r te fico H He Use IMU raw data rate Binary hi res output rate This field determines the rate that epochs are written to the binary solution files These files are used during the output process in Export Wizard T 3 Gees Apply and so the value entered here depends on the final output interval required Lowering this drastically reduces file sizes Use IMU raw data rate This option forces the binary files to be written at the mechanization rate and it is only recommended to out
102. o determine its usefulness Measurement standard deviations The standard deviation associated with the DMI measurements depend on the DMI being used As such this value may need to be determined empirically Wheel circumference The default value is 1 96m Change this value if it is not correct Small errors are compensated for by the computed scale factor during processing It is also possible to allow the software to determine this value based on the header in the DMR file assuming such information is available 32 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Mount If you have mounted your IMU onto a gyro stabilized platform you will need to provide Inertial Explorer with the angular rotations to compensate for the changing lever arm between the IMU and GPS Advanced Sensor Body Rotations Many typical IMU installations have the surface of the IMU directly attached to the floor of the vehicle so the sensor frame of the IMU and the body frame of the vehicle are more or less aligned In these installations the roll pitch and yaw of the vehicle are directly sensed by the IMU Some IMUs are installed in a tilted position with respect to the body frame of the vehicle If the tilt between the IMU frame and body frame is known Inertial Explorer compensates so that the attitude information produced is with respect to vehicle body frame not the IMU sensor frame The order of rotations empl
103. o the clipboard In GrafNav and GrafNav Batch users can create groups of plots that can be displayed using one operation Multiple plots can also be selected and for all plots time and y axis ranges can be applied from one plot to others For GrafNav there is now an API DLL that has many of the same capabilities as command line the command line interface but the calling application is provided complete feedback during processing and exporting The export wizard has improved time zone selection for local times and hour time zones are now supported A variety of HTML reports can now be generated including from the command line and API GrafNav command line and API permits users to save all processing messages to a single log for later review GrafNav and GrafNet project data can be automatically displayed in Google Earth In GrafNet the network adjustment can now execute automatically on completion of processing and it now supports station names as long as 12 characters The Favorites Manager has been significantly improved such that nearby stations are shown in a list along with the distance and datum Furthermore antenna attributes can be stored and selected There is now support for stereographic map projection and Processing files can now be deleted recursively in subdirectories from a specified path Version 8 10 has full support for ITRF2005 and improved software registration Decoder improvements e For Leica 1200 better handling o
104. ocess Menu Refer to the GrafNav GrafNet Version 8 20 Manual for information regarding all of the features available via this menu Only those features that are exclusive to Inertial Explorer are discussed here 1 5 1 This window provides access to most settings related to loosely coupled IMU processing Process IMU loosely coupled System Processing Direction Forward and reverse IMU processing is possible in Inertial Explorer This option defines in which direction through time the data is to be processed The different processing directions are listed m the shaded box GNSS IMU Processing Profiles Choose IMU Profile Option Select an appropriate profile from the drop down menu prior to processing This ensures that the GNSS and IMU settings are configured in an optimal way Make adjustments to the settings as needed To see what each profile s configuration looks like click the Profile Manager button 24 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Lever Arm Offset IMU GNSS Antenna In order for the GNSS updates to be performed accurately enter the 3 D offset from the center of the IMU sensor array to the GNSS antenna This offset vector must be entered with respect to the body frame of the vehicle as the image in the shaded box shows Save lever arms for future access with the Favorites button Read lever arms from IMR file If lever arm values are written
105. on the dynamics at the chosen start time This feature is useful in the presence of large data gaps While Inertial Explorer has been successful at aligning tactical grade systems using this method there is no guarantee regarding lesser grade IMUs It might even be necessary to pick a different error model in order to prevent instabilities arising in the Kalman filter Initial Static Alignment Period The length of time assigned to static alignment depends on the method of alignment being used In all cases it is important that the values entered are in accordance with the Begin and End times specified under the General tab To perform a static alignment specify the length of time that the IMU was stationary If this is unknown the Velocity Profile plot obtained from the GNSS processing is useful If selected the time used for fine alignment is determined by differencing the Total and Coarse time fields This field does not apply for transfer alignment or for kinematic alignment IMU Processing Settings 4 221 x DMI Error Model User Cmds System General Reverse GNSS Advanced M Se Mount Forward ii Static coarse fine alignment C Transfer alignment enter known attitude Enter Attitude Kinematic alignment m Initial Static Alignment Period r Initial Position and Velocity Determine from GNSS suggested Use entered values IMU only using trajectory Coarse 6
106. over ZUPT length seconds Default is 1 Minimum length of time for a ZUPT Reject a ZUPT with velocity above this tolerance in m s 87 Appendix A Inertial Explorer 8 20 User Guide Rev 6 Appendix A 88 A accelerometer 19 28 36 Add 22 Master File s 22 Remote File 22 Alignment discussion 68 methods 28 antenna frame 25 height 22 lever arm 20 25 45 profiles 47 reference point ARP 22 station height 23 Auto Start Description 22 how to use 22 B BIF File data structure 61 BIR File data structure 61 Body Frame description 64 Boresighting Angles 40 Description and FAQ 71 Input formats 43 BTF File data structure 61 BTR File data structure 61 C coarse alignment description 28 combining solutions forward and reverse smoothed 39 Computation Frame description 64 Convert GNSS Data 20 IMU Data 20 Converting creating profile for raw data conversion 50 raw IMU data to IMR 49 Coordinate Frames discussion 63 D data interval Inertial Explorer 8 20 User Guide Rev 6 for GPS updates in Inertial Explorer 26 for IMU processing 26 DMI Options 32 DMR File 56 E Error Model discussion 67 error model creating 36 settings 35 Export Final Coordinates 21 export wizard 45 F FIL File see Message Logs 59 File Data Coverage Determine Alignment Method 20 IMU alignment 78 Load 20 FIM File see Trajectory File 60 fine alignment description 28 FTL Files
107. oyed is R then Ry followed by R Initial Accel Biases Gyro Drift Values Inertial sensors tend to contain biases that can be defined as long term constants In cases involving tactical or navigation grade units these values are calibrated by the manufacturers Enter these biases here to allow Inertial Explorer to remove them from the Av and AQ measurements during processing Calibrations can be performed here and used for subsequent missions The highest accuracies are achieved for those inertial units with predictable and known turn on to turn on biases However the methods of rigorously calibrating inertial sensors with off line procedures involving rate tables are outside the scope of the Inertial Explorer software Ensure that any values entered here are in the required units and are with respect to the body frame See What is a body frame on Page 64 for a definition of the body frame for Inertial Explorer If the IMU has a different sensor frame definition that is a sensor frame which is not coincident with the body frame of the vehicle ensure that the biases in the pitch axis are entered in the X axis fields with the appropriate sign The bias in the roll axis should be entered into the Y axis fields and those for the yaw axis should be entered into the Z axis fields IMU Processing Settings 21x System General Forward Reverse GNSS Advanced Error Model DMI Mount UserCmds Import Brow
108. pensate for large biases in the accelerometers Gyro Drift Gyroscope drift densities similarly act as additives to the covariances computed for the gyroscope drift states In the case of inexpensive units larger values here may be necessary IMU Processing Settings 2 x System General Forward Reverse GNSS Advanced DMI Error Model User Cmds Error Model Select error model m Initial Standard Deviation Values Misalignment fi 1111e 002 fr 1111e 002 27778e 000 deg Accel Bias g 0000e 004 B 0000e 004 3 0000e 004 metres s 2 Gyro Drift 2 7778e 006 2 7778e 006 2 7778e 006 deg s r Spectral Densities Values square root of Misalignment 2 7778e 004 27782004 27785004 deg s Accel Bias 2 1623e 006 8 1623e 006 beem metres s 2 Gyro Drift 8 7841e 010 7841e 010 7841e 010 deg s Velocity f1 0000e003 f1 0000e 003 f1 0000e 003 m s Position fr 0000e 003 fr 0000e 003 fr 0000e 003 m Inertial Explorer 8 20 User Guide Rev 6 37 Chapter 1 Inertial Explorer IMU Processing Settings 21x System General Forward Reverse GNSS Advanced DMI Mount Error Model User Cmds m Error Model Select error model Inertial Sciences ISIS JAMI Litton LN 200 Edit MotionPack Add From Remove Initial Standard Deviation Values Misalignment fr iiiieo02 friitteo02 27778e 000 deg 3 0000e 004 3 00006 004 3 000
109. photos are not used by the module The formats which include these variables are only supported to facilitate the import process if you do not wish to go through the trouble of removing those fields from your input files beforehand Import Photo EO WPK Angles F xl Fenme Browse File format ID omega phi kappa E ven v Attitude units Degrees e Inertial Explorer 8 20 User Guide Rev 6 43 Chapter 1 Inertial Explorer Plot Description Accelerometer Bias Table 1 IMU Plots This is the apparent output in acceleration when there is no input acceleration present It is computed by the GNSS INS Kalman filter and the effects may be sinusoidal or random It is plotted in terms of the X right direction Y forward direction and Z up direction of the INS body Generally they should stabilize after the alignment period and agree when processed in both directions Attitude Azimuth Heading Plots the heading and GNSS COG course over ground that was computed from the GNSS INS processing Effects of crabbing is visible in this plot if the GNSS COG bears a constant offset from INS heading The IMU Heading COG Difference plot shows the difference between these two heading values Note that any transitions between a heading of 359 degrees and 0 degrees shows up as a vertical line Attitude Roll and Pitch Plots the roll and pitch values from GNSS INS processing In airborne data it i
110. pled about 12 FAQ 81 Processing 38 time range processing range in Inertial Explorer 26 Trajectory File format and description 60 Transfer alignment Description 29 U updates coordinate 34 GPS source file 30 GPS velocity 31 zero velocity 34 User Defined Options adding commands 38 list of commands 85 User interface improvements 11 V Variance factors 30 Z ZUPTs description 34 using 80 Inertial Explorer 8 20 User Guide Rev 6
111. poch typedef struct double Time long 9x 9y 9Z long ax ay az INS type GPS time frame seconds of the week delta theta or angular rate depending on flag in the header delta v or acceleration depending on flag in the header this is the binary structure type expected in GPSIMU lt The angular increments or angular rates are scaled long integers The scale factor to obtain a double precision word must be supplied in the header Similarly the accelerations or velocity increments are signed four byte words and must be scaled by a double precision variable given in the header Inertial Explorer 8 20 User Guide Rev 6 55 Chapter 3 Data and File Formats 3 22 DMR File All odometer data must be written into Waypoint s generic format DMR before it can be used within Inertial Explorer struct dmi hdr type char szHdr 8 short sHdrSize short sRecSize short sValueType short sMeasType short sDim short sRes short sDistanceType short sVelocityType double dScale S DMIRAW 0 NULL terminated ASCII string Size of header in bytes Must be set to 512 Size of each record refer to dmi lrec type and dmi drec type 12 8 sDim if sValueType DMI VALUE DOUBLE 1 12 4 sDim if sValueType DMI VALUE LONG where sDim is number of DMI sensors Number type DMI VALUE LONG DOUBLE 0 if logging data using LONG values 1 if loggin
112. points and a minimum of four control points although more can be very helpful e Scale is not so important but should match typical flying scales Very large scales lt 1 8000 may result in less accurate boresighting angles due to increased influence by GNSS positioning errors GNSS and IMU data that contains camera event marks Images must have been properly time tagged by GNSS IMU system e A GNSS only processed solution initially e A valid bundle adjustment solution using these tie and control points as well as the GNSS camera centre positions Although using the GNSSposition is not necessary it is highly suggested to decorrelate the image position and attitude e Exported omega phi kappa in a format compatible with this module The naming convention used for the photo IDs must match that used in Inertial Explorer e A fully processed Inertial Explorer project with a forward reverse combined or smoothed IMU solution loaded 4 44 Can I use this module to boresight my pushbroom or laser data No this module only works with frame imagery 4 4 5 Does this module come witha bundle adjustment No you must use an external package to determine the omega phi and kappa angles for each image 4 4 6 What do I need to get started What you need to utilize this module is listed in the shaded box 4 4 7 What if my photo angles are not omega primary phi secondary and kappa tertiary Currently
113. pro e RE 82 4 11 4 Should I use loosely coupled or tightly coupled processing xmmnrnna 83 4 12 Data Analysis TIPS 41444 nisana kaabel aadu tv ala AAA a katu a 83 4 12 1 How is the IMU quality Q number different from the GNSS Q number 83 4 12 1 What plots should I examine after IMU Processing minnnnenenanannaannnanannna 84 4 12 3 How do I smooth and export data nmeennnnannnnnnnnnanaanannnnnnanaaanaaanann naa 84 4 Inertial Explorer 8 20 User Guide Rev 6 Table of Contents Appendix A Summary gell Ee E Index Inertial Explorer 8 20 User Guide Rev 6 Table of Contents Inertial Explorer 8 20 User Guide Rev 6 List of Figures Body Frame Definition for Lever Arm Offset EEE EEE EEE 25 Coordinate Frames in Inertial Explorer mrenneenennrennnnnenannnenaanneeennaennanaananannnaananaa annan 63 Body Frame Definition vu usanummusnmvbheidukndaenruuenGukuneddte kuttene 64 IMU Gamera sv isitutyedtdndumride krank aka adu aka aaa M Amkar amb am i eha sauen danene 67 Inertial Explorer 8 20 User Guide Rev 6 List of Tables IMU Ae i 44 Binary Structure of Raw Data verenennenenanaenannnnnnannaananannananaananannananaanaa anna EASE EnEn Ennn n nna 53 Pitch and Yaw RI EE 70 Inertial Explorer Extensions for Output Files Inertial Explorer 8 20 User Guide Rev 6
114. project using Auto Start con t 5 Check the Start processing page right away box and click OK to process the GNSS data Refer to Chapter 2 of the GrafNav GrafNet Version 8 20 Manual for more information on GNSS processing 6 Select File Add IMU File The IMU data must be concurrent with the master and base station and remote data To verify this click the Plot Coverage button to display the File Data Coverage plot This step is not necessary if you are auto starting lt The IMU data must be converted to the IMR format before being added to the project Choosing a name of an existing project overwrites that project 7 Choose the DMR file If any DMI data is available select the Enable DMI data option This data must be collected concurrently with the rest of the data in the project Use the Plot Coverage button to find overlapping DMR data 8 Choose an Error Model Several error models are available during GNSS IMU processing For the best results select the profile that is most suitable to the IMU being used 9 Enter the Master Station Coordinates 10 Enter the Remote Station Antenna Height This antenna height applies primarily to kinematic trajectories It is overridden by features stations events and static sessions To change the antenna height on static sessions select View Objects KAR Static then select Edit for each static session Iner
115. pter 2 on Page 49 for details manufact imu Contains the error profile parameters for various types of IMUs The values associated with each model have been empirically derived by the Waypoint Products Group staff based solely on the data sets they have encountered manufact dcb List of the differential code biases in nanoseconds between the P1 and C A code for each satellite Used by PPP Inertial Explorer 8 20 User Guide Rev 6 47 Chapter 1 Inertial Explorer 48 Inertial Explorer 8 20 User Guide Rev 6 Chapter 2 Conversion Utilities 2 1 Raw IMU Data Converter The IMU Data Converter utility is a Win32 application program that converts custom data formats into a generic raw IMU data format which is described in Section 3 2 1 on Page 54 of this manual This utility is available exclusively to users of Inertial Explorer and may be accessed via File Convert Raw IMU Data to Waypoint Generic IMR 2 1 1 Waypoint IMU Data Conversion Input Output Files Refers to the names and locations of all input and output files Input Binary IMU File Click the Browse button to locate the raw IMU data file Output Waypoint Binary File By default the binary output file created are given the same filename as the input file but with an IMR extension It will be saved to the directory containing the input file Output Waypoint ASCII File If the Output ASCII option is enabled the utility generates an ASCII fi
116. put at this rate Inertial Explorer 8 20 User Guide Rev 6 27 Chapter 1 Inertial Explorer IMU Processing Settings DMI Mount Error Model User Cmds 21 xi System General Forward Reverse GNSS Advanced m Method for Initial Alignment C Static coarse fine alignment Transfer alignment enter known attitude Enter Attitude Kinematic alignment Initial Static Alignment Period gt r Initial Position and Velocity Ze Determine from GNSS suggested C Use entered values IMU only Fine 0 00 s using trajectory Total E 00 fs Coarse 60 00 s Source of GNSS Updates Update data GNSS Combined missing Mi Browse External File name C XDocuments and Settings nfoss Desktop Desktop Airbor Cancel Apply IMU Processing Settings DMI Mount Error Model User Cmds 21x System General Forward Reverse GNSS Advanced m Method for Initial Alignment C Static coarse fine alignment Transfer alignment enter known attitude Enter Attitude Kinematic alignment r Initial Static Alignment Period gt r Initial Position and Velocity Determine from GNSS suggested E G 50 00 SS 9 Use entered values IMU only Fine 0 00 s using trajectory Total 60 00 fs r TE of GNSS Updates Update data GNSS Combined missing zl Browse External File name EADocuments and Settings nfoss Desktop Desktopirbor
117. r information to compute GNSS 21x derived velocities DMI Mount ErorMode UserCmds System General Forward Reverse GNSS Advanced Doppler accuracies vary si gnificantly r Variance Factors for residuals Extra GNSS Updates depending on the receiver View the L Doppler GPS Position 20 IV Enable GNSS velocity update Residual RMS via Output Plot Results The I Enable Noisy Phase Measurements standard deviation of the Doppler 120 IV Enable Heading Updates from File measurements used by the GNSS Kalman filter can be controlled via Settings Individual PhaseMeas 1000 Measurements Bronse Std Dev Heading deg 0 000 Enable GNSS velocity update Enabled by default Disabling this eliminates the Boresight RotatonZ deg 0000 use of GNSS velocity information for updates Enable Noisy Phase Measurements When applying phase updates Inertial Explorer performs two quality checks Firstly the measurements must have locktimes equal to or greater than the locktime cutoff For more information refer to the Avanced I tab in the GrafNav GrafNet 8 20 Manual Secondly Inertial Explorer performs its own cycle slip detection by comparing the observed change in the carrier phase measurements over one epoch with the expected change from the Doppler measurement If the observed change in carrier phase exceeds that of the Doppler cycle slip check the phase measurement is rejected This option disables Inertial
118. r is forced to work in prediction mode which generally causes the position errors to grow exponentially However significant positioning errors can also occur from the presence of poor quality GNSS data The smoothing algorithm implemented was derived by H Rauch K Tung and C Striebel and hence is often referred to as the RTS smoother This smoothing process works backwards which therefore implies that data must exist at the epoch after the one being smoothed The RTS algorithm employs a fixed interval technique meaning that the entire data set is smoothed at the same specified interval 70 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 As previously mentioned this backwards smoothing procedure can be very advantageous for those data sets where the GNSS data is missing The algorithm uses the data from the last epoch and works backwards to compute new states for each epoch As such an improvement in the results is especially noticeable if a good solution is available immediately following an outage The maximum magnitude of the position error during a GNSS data gap can be greatly reduced by applying this RTS smoother This feature smooths positions velocities and attitude See Section 1 5 3 on Page 39 for help using the RTS smoother 4 4 What do I need to know about Boresighting 4 4 1 Why is boresighting needed Generally the IMU and imaging system can never be per
119. rformed from within the same project Refer to the following question for more information 4 11 3 How can I differentiate between the files created by loosely coupled and tightly coupled processing Inertial Explorer assigns a different set of extensions to the output files to ensure that both methods of processing can be employed without over writing any files Please see Table 4 in the shaded box for additional information Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 4 11 4 Should I use loosely coupled or tightly coupled processing In the presence of good quality open sky data tightly coupled processing is of little if any benefit over loosely coupled processing It is therefore generally recommended that this latter method of processing be used for data sets collected in good GNSS conditions particularly airborne projects Tightly coupled processing is strongly recommended for ground vehicle data sets where satellite tracking is often poor due to physical blockages such buildings or trees In such situations the chances of four satellites being tracked may be low meaning that the updates would be sparse if processing using the loosely coupled methodology The tightly coupled processor can use as few as two satellites to generate updates making it ideal in these poor tracking environments 4 12 Data Analysis Tips There are a number of key graphs and indicators which must be ex
120. roducts Group is attempting to update this file on a regular basis as more information about the different sensors on the market is obtained especially in the MEMS category Inertial Explorer 8 20 User Guide Rev 6 67 Chapter 4 FAQ and Tips 4 3 2 Why is alignment so important Alignment is the process of computing the initial values of roll pitch and yaw proper alignment is very important to IMU performance and processing because errors result directly into attitude errors which can take some time to correct by the Kalman filter Alignment can either be static or kinematic although the former is recommended Static alignment generally takes place in two stages with the first being coarse alignment and the second being fine alignment Coarse alignment is a requirement for static alignment whereas fine alignment is optional If the you have GNSS data immediately available for updates the static fine alignment process can often be ignored 4 3 3 What is static alignment Coarse alignment generally requires to 2 minutes of static data The default time for coarse alignment in Inertial Explorer is 120 seconds The software monitors the data and warns you if kinematic data is detected During coarse alignment the basic signal from a set of static accelerometers is the gravity vector In this B frame definition roll is a function of acceleration as measured in the X axis of the body Pitch is a function of sensed accel
121. roducts or use in other than a normal and customary manner environmental conditions not conforming to NovAtel s specifications or failure to follow prescribed installation operating and maintenance procedures 11 defects errors or nonconformities in the Products due to modifications alterations additions or changes not made in accordance with NovAtel s specifications or authorized by NovAtel iii normal wear and tear iv damage caused by force of nature or act of any third person v shipping damage vi service or repair of Product by the Purchaser without prior written consent from NovAtel vii Products designated by NovAtel as beta site test samples experimental developmental preproduction sample incomplete or out of specification Products viii returned Products if the original identification marks have been removed or altered or ix Services or research activities 7 EXCLUSION OF LIABILITY If a Party would but for this paragraph 7 have concurrent claims in contract 18 and tort including negligence such claims in tort including negligence shall to the extent permitted by law be wholly barred unenforceable and excluded NovAtel shall not be liable to the Buyer by way of indemnity or by reason of any breach of the Order or of statutory duty or by reason of tort including but not limited to negligence for any loss of profit loss of use loss of production loss of contracts or for any financing costs or for any i
122. rrennnnnnnrenrennnnnnnnennrenannrnnnennresnnrnnnennnne 71 4 4 2 How does the boresighting module work uarsrrnrrrrrrnnnrnnnonrennnnrrnnrnnnnennrrenrnnrenrrrrnnnnnnnnnennn 71 4 4 3 What are omega Phi and kappa mtenannnennennaaanaanannannnaanaananannnnnaaanaa nan 71 4 4 4 Can I use this module to boresight my pushbroom or laser data 0 me 72 4 4 5 Does this module come with a bundle adjustment Wu u u ssseeeeeee nerne renerne nr nn nen 72 4 4 6 What do I need to get started inmenennnenanaaaanannaanaaannaannannanananaannenananaaaananna 72 4 4 7 What if my photo angles are not omega primary phi secondary and kappa tertiary 72 4 4 8 Where is my boresighting file data stored nsmennenenaananannannananaanna annan 72 4 4 9 What if Inertial Explorer does not support my grid System marnnvnnrnrrnnnnnnvnnrnrrnnnnnnnnrnnnn 72 4 4 10 What mathematical equations are used by boresiobting erne reren renee 73 4 5 How do I decode raw inertial data mnnennennanananennnanannannneenanaaanaanananananaaaanaa nan 74 4 5 1 How do I deal with offsets between IMU sensor frame and vehicle body frame 74 4 6 How do I deal with an upside down IMU seas eeeeaeesecaeeeseaaeeeeeeeeseaaeeeeeeeeess 75 4 7 How do deal with unknown lever arm offsets from an IMU centre to a GNSS an
123. rved for additional information zero at creation of new file normal record definition Inertial Explorer 8 20 User Guide Rev 6 61 Chapter 3 Data and File Formats typedef struct double GpsTime short WeekNum short Reserved plh_type GeoPos fxyz_type LLVel fxyz_type LLAcc iatt_type LLAtt fxyz_type LLAttDot float fPosTrace float fVelTrace float fAttTrace imu_outrec_type 92 bytes GpsTime of this record 0 604800 week number reserved for future flags geographic position of this record deg m local level velocity m s local level acceleration m s local level attitude deg scaled body frame rotational rate deg s trace of position covariance m trace of velocity covariance m s trace of attitude covariance deg 62 Inertial Explorer 8 20 User Guide Rev 6 Chapter 4 FAQ and Tips 4 1 Overview of FAQ and Tips The following sections offer suggestions on how to get started process and analyse GNSS IMU data in Inertial Explorer Here you will find tips regarding common problems such as data decoding error modelling alignment processing and analysing results center of mass of the Earth 4 2 How are Inertial Explorer and coordinate frames related Inertial navigation is mainly concerned with spin axis of the Earth coordinate frames Inertial sensors measure the rate information relative to an inertial
124. s are achieved 4 9 4 How can I use transfer alignment Transfer alignment requires that a forward or reverse IMU file is present containing pre determined coordinate attitude and covariance information Alternately this information can be entered for a particular time Transfer alignment should be chosen at the present time as a last resort 4 10 Processing Tips For users operating in a good GNSS environment processing should be relatively straightforward provided the correct IMU Error Model has been chosen Nevertheless there are some input options which may be considered if the initial data processing has appeared to have quality problems Inertial Explorer 8 20 User Guide Rev 6 79 Chapter 4 FAQ and Tips 4 10 1 How do I use ZUPTs Inertial Explorer automatically detects the presence of ZUPTs by analyzing the GNSS IMU and if available DMI data This is true for both loosely and tightly coupled processing As such the manual entry of ZUPTs is generally not necessary except in cases of poor data quality Consult the IMU Status Flag plot after processing to determine the periods where a ZUPT was detected If a known ZUPT was missed you can manually enter it using the Advanced Tab 4 10 2 I only have a single point solution FSP File is this okay This is fine but please make sure that you do not use GNSS Velocity updates Turn this option OFF under the GPS dialog tab 4 10 3 Does 10 Hz G
125. s common to see roll values between 30 degrees and pitch values of around 10 degrees depending on the flight pattern of the aircraft itself This plot shows the difference between the forward and reverse solutions in terms of roll pitch and heading A zero Attitude separation is ideal as it indicates matching solutions in the Separation forward and reverse IMU processing Spikes at the beginning and the end of the plot are common as they indicate the periods of alignment This plot presents the DMI scale factor as computed by the DMI Scale Kalman filter It should be loaded separately for forward and Factor reverse processing to ensure that the same scale factor is computed in both directions Ideally the plotted line should be horizontal indicating a constant scale factor DMI Residual This plot presents the difference between the computed displacement or velocity and that reported by the DMI Estimated This shows the estimated standard deviation of the Accelerometer Bias Accuracy Estimated Attitude Accuracy accelerometer bias It is plotted in terms of the X right direction Y forward direction and Z up direction of the INS body This plot shows the standard deviation computed in the GNSS INS Kalman filter in terms of roll pitch and heading Estimated Gyro Drift Accuracy This plot shows the estimated standard deviation of the gyro drift rate which generally decreases with time It is plotted in
126. se mount data must be in standard format and reference use Import Info m Additional Corrections IV Enable external auto stabilized camera mount input using file I Apply IMU to Camera boresight angles as solved by Inertial Explorer Omega Phi Kappa Io PK I Apply Mount to Body frame correction normally 0 0 0 Hat Roty Hetz order is Y2 degrees SR IMU Processing Settings 2 x User Cmds Advanced DMI Mount Error Model System General Forward Reverse GNSS r Sensor gt Body Rotation Initial Accel Biases p Initial Gyro Drift Values Rotate IMU to vehicle T Manual value entry Manual value entry Ideal m s 2 deg s Rot Dong yRot Dong 2Rot 0 0000 Z m Zero Velocity Updates ZUPTS Name Startts Endis 4 gt 4 gt Add Edt Remove Load Add Edt Remove Load m Heave Compensation for Height IV Apply Heave 30 0 Window seconds SR Inertial Explorer 8 20 User Guide Rev 6 33 Chapter 1 Inertial Explorer IMU Processing Settings DMI Mount Error Model User Cmds System General Forward Reverse GNSS Advanced r Sensor gt Body Rotation gt r Initial Rotate IMU to vehicle I M deg Rot 0 0000 yRot 0 0000 2Rot 0 0000 Accel Biases r Initial Gyro Drift Values anual value entry I Manual value entry m s 2 deg s Name Starfs Endis Z
127. ses Inertial Explorer reads the CMB file by default and stores the coordinate velocity and associated covariance information in a binary image in memory Generally IMU measurements and GNSS epochs are not aligned Therefore Inertial Explorer interpolates the inertial records either side of the GrafNav time tag to line up a derived inertial measurement with the corresponding GPS time At this derived point the mechanized inertial coordinates and velocities are differenced from the GNSS computed quantities to obtain the error in the inertial information These estimated errors are used as update information in the IMU Kalman filter The covariance information from the GrafNav file is used as weighting in this update procedure DA Section 1 5 1 on Page 24 discusses the GNSS tab and provides the opportunity to reject GrafNav information which is deemed unacceptable for updating purposes Rejection tolerances can be based on ambiguity determination standard deviation or quality number Tolerances are based on the stand alone navigation capabilities of the inertial system Covariance can also be scaled 4 3 6 What is Kalman filter smoothing Inertial Explorer offers the opportunity to perform Kalman filter smoothing on their GNSS IMU data While this feature is aimed primarily at datasets suffering from GNSS outages it can be used in virtually any circumstance where position errors are large Without GNSS updates the Kalman filte
128. tegrate the data from distance measurement instruments DMI engage the Enable distance measurement odometer updates to access the options File Use the Browse button to locate the DMR file containing the measurements from the DMI Once a valid file has been selected the software scans it to detect how many sensors were used Use Info to view information concerning the selected file Sensor s Displays the sensors with data that is used during processing The number of these entries depends on how many sensors were detected in the DMR file and whether or not they were all incorporated Use the Add button to include any sensors in the DMR file which were previously being excluded Use the Remove button to eliminate the use of a specific sensor s data Use the edit button to modify the lever arm values relating the IMU to a specific DMI Settings The following settings pertain to the added DMR file DMI observation treatment A typical DMI will either output a tick count or a velocity vector If tick counts are recorded Inertial Explorer converts them into velocity vectors If velocity vectors have been recorded then the software uses them as such Automatically detect ZUPTs from DMI sensor A DMI can often be used to determine periods of zero velocity which can help improve accuracies The performance of this feature is dependent on the type of DMI being used so it is suggested to process data with and without this option t
129. tenna 75 4 8 How important is error model tuning nnrennnnnannannenanananaannennaanaanaannnananaaaaaaana nan 76 4 8 1 How do I build my own error model 77 4 8 2 How do I know if my error model is working mnnrennannenennnennannaenananna anna 77 4 9 How can I use the alignment of the IMU Wu u u u u dsseeeeeere renere kreere renerne 78 4 9 1 How much static alignment data do need mrennnennnnnannannnennanaanaannnna 78 4 9 2 How do I find start end times for the IMU alignment mtmnnmnnennannnanana annan 78 4 9 3 How can I use kinematic alonment nerne renerne reen 79 4 9 4 How can I use transfer alignment ennen renerne renerne 79 4 10 Processing RTE 79 4 10 1 How do I use ZUPTS EE 80 4 10 2 I only have a single point solution FSP File is this okay c ccecceeeeseseeeeeeteeeeeneeeeees 80 4 10 3 Does 10 Hz GNSS data help sssrini anaana aa a an da iaaa 80 4 10 4 What should I look for while the IMU data is processing arrrnnnnnvnnrnrrvnnnnrnnnenrrennnnnnnrnnnn 80 4 11 Tightly Coupled Processing Tips 81 4 11 1 What is the difference between loosely coupled and tightly coupled processing 81 4 11 2 How do I engage loosely coupled and or tightly coupled processing in Inertial Explorer 82 4 11 3 How can I differentiate between the files created by loosely coupled and tightly coupled
130. tial Explorer 8 20 User Guide Rev 6 23 Chapter 1 Inertial Explorer IMU Processing Settings 21 x DMI Mount Error Model User Cmds System General Forward Reverse GNSS Advanced User Me r Processing Direction Both Forward C Reverse GNSS AMU Processing Profiles I Choose IMU Profile Option Profile Manager Last Profile Loaded 1 4 View Menu Refer to Chapter 2 of the GrafNav GrafNet Version 8 20 Manual for a description of all the features available in this menu lt In Inertial Explorer view IMU message log and trajectory files under View Forward Solution and View Reverse Solution See Section 3 2 on Page 54 for information on file formats m Lever Arm Offset IMU gt GNSS Antenna Value Initial SD x 10 000 E 000 m z Y 0 000 5 000 m TZ Z 0 000 5 000 m Favorites I Read lever arms from IMR file Enter Manually I Solve lever arm values as additional kalman filter states Processing Directions Forward Processes data chronologically starting from the beginning and in same direction as it was collected Reverse Processes data set backwards meaning it starts at the end and stops at the beginning Both Processes data in both directions sequentially or for computers with dual processing capabilities simultaneously Assuming the appropriate option is enabled the two solutions are combined 1 5 Pr
131. to the header of the IMR file then use this option to extract them Solve lever arm values as additional Kalman filter states Use this option if the 3 D offset from the center of the IMU sensor array to the GNSS antenna is not precisely known or not known at all The accuracy achieved with this option depends on the type of IMU used but is normally better than 20 cm General File Info The following fields are displayed IMU file Displays the path to the binary IMU measurement file that was added to the project If incorrect go to File Add IMU File to locate the proper raw data file Process The following options are available Process IMU data only This option enables disables the use of GNSS data during IMU processing lt This mode of processing is not recommended because it is only used for special applications Output binary values for smoother This option ensures that the files required to use the RTS smoother are written to disk To save disk space and not run data through the smoother disable this option Figure 1 Body Frame Definition for Lever Arm Offset The IMU is the local origin of the system and the measurements are defined as the following X The measured lateral distance in the vehicle body frame from the IMU to the GNSS antenna Y The measured distance along the longitudinal axis of the vehicle from the IMU to the GNSS antenna Z The measured height change from the IMU to
132. ts Y forward and the positive Z axis of the vehicle body frame points up Make sure the positive sense of the rotation angles matches the positive sense of the vehicle body frame If the you rely on the Sensor Body Rotation options under the Advanced tab of the IMU processing settings then a rotation about the Y axis of 180 is needed to rotate an upside down IMU into the Inertial Explorer vehicle body frame 74 Inertial Explorer 8 20 User Guide Rev 6 FAQ and Tips Chapter 4 4 6 How do I deal with an upside down IMU In principle Inertial Explorer should not have any problems processing data where the sensor frame of the IMU is mounted at any odd set of angles with respect to the vehicle body frame However the final output attitude information is most likely be pointing in the wrong direction Most IMUs have the sensor frame inscribed on the IMU box To obtain an output of roll pitch and heading relative to the positive motion of the vehicle or aircraft then the IMU sensor frame must be mounted parallel to the body frame of the vehicle Alternatively a profile which fools the IMU data converter into thinking the sensor frame has been mounted parallel to the body frame can be defined The final or enter rotation angles into the Advanced Dialog Box Otherwise you will output azimuth to for example the wing tip not the forward longitudinal axis of the aircraft Your roll and pitch might be mi
133. ucZ char szProgramName 32 time_type tCreate bool bLeverArmValid long IXoffset long lYoffset long IZoffset char Reserved 354 D Defines whether the GPS time tags are on the nominal top of the second or are corrected for receiver time bias 0 do not know default is corrected time I receive time on the nominal top of the epoch 2 corrected time i e corr_time rev time revr clock bias default is 0 0 but if you have a known millisecond level bias in in your GPS INS time tags then enter it here Name or type of inertial unit that is being used Set to true if the sensor definition that follows is valid Skip if writing directly to this format Direction of X axis skip if writing directly to this format Direction of Y axis skip if writing directly to this format Direction of Z axis skip if writing directly to this format Name of calling program skip if writing directly to this format Creation time skip if writing directly to this format 12 bytes Set to true if the sensor definition that follows is valid Lever arm is from IMU to GPS phase centre X value of lever arm in millimeters Y value of lever arm in millimeters Z value of lever arm in millimeters Reserved for future use bytes should be zeroed The single header which is a total of 512 bytes long is followed by a structure of the following type for each IMU measurement e
134. ufacturers Sensor Orientation x Right Side Y Front Positive Pitch Rate Positive Roll Rate Z Up Positive Yaw Rate r Define the IMU manufacturers sensor system Select orientation of X AXIS in the sensor frame New Sensor Definiton Select K lt Clear Y e Update z Available Orientations Inertial Explorer will rotate this system into a Y forward roll rate X right side pitch rate Z up paw rate definition How to define the orientation of the IMU 1 Specify the X direction by selecting the direction that corresponds to the X axis of the sensor frame 2 Click Select to set that direction to the X axis 3 Specify the Y direction next by selecting the direction that corresponds to the Y axis of the sensor frame 4 Click Select to set that direction to the Y axis B Given the constraint that the frame is right handed this direction will be automatically determined by the software 5 Click Update to apply the new sensor orientation to the profile lt Ifa mistake is made at any point during the process click Clear to start over 6 Click OK to save the new profile lt It should immediately appear in the scroll down list under the IMU Profiles box of the main window Inertial Explorer 8 20 User Guide Rev 6 51 Chapter 2 Conversion Utilities 52 Inertial Explorer 8 20 User Guide Rev 6 Chapter 3 Data and File Formats
135. ver to the Licensee and the Licensee will indemnify and hold NovAtel harmless against all or any loss damage actions costs claims demands and other liabilities or any kind whatsoever direct consequential special or otherwise arising directly or indirectly out of or by reason of the use by the Licensee of the Software whether the same shall arise in consequence of any such infringement deficiency inaccuracy error or other defect therein and whether or not involving negligence on the part of any person 8 Disclaimer and Limitation of Liability a THE WARRANTIES IN THIS AGREEMENT REPLACE ALL OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE NovAtel DISCLAIMS AND EXCLUDES ALL OTHER WARRANTIES IN NO EVENT WILL NovAtel s LIABILITY OF ANY KIND INCLUDE ANY SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES INCLUDING LOST PROFITS EVEN IF NOVATEL HAS KNOWLEDGE OF THE POTENTIAL LOSS OR DAMAGE b NovAtel will not be liable for any loss or damage caused by delay in furnishing the Software or any other performance under this Agreement c NovAtel s entire liability and your exclusive remedies for our liability of any kind including liability for negligence for the Software covered by this Agreement and all other performance or non performance by NovAtel under or related to this Agreement are to the remedies specified by this Agreement 9 Governing Law This Agreement is gover
136. verse mp on reg d ee 9 y ports Run RTS smoother on Loosely Coupled both directions prese D relevant exclusively to Inertial Explorer are made here Combine Smooth IMU Forward and Combine Settings Reverse r Smoother Settings Inertial Explorer is capable of combining processing Direction s to smooth directions and or performing Kalman filter smoothing 2 Jr on inertial trajectory This option reguires that the paee E Smooth both directions and combine inertial data is already processed r Time Range Smoothing provides the most significant results on I Process entire time range those data sets where GNSS outages were a problem Sta 236858 0 s TOW 1380 week By using this smoother the position velocity and End 240719 0 s TOW 1380 week attitude errors can be reduced when GNSS updates are not available Smoothing can also clean up position and Cancel velocity accuracies even if there are no gaps See Chapter 4 on Page 63 for more information Function to perform Two options available are the following Combine forward and reverse This option combines the FIM and RIM as well as the FTM and RTM files that were produced during GNSS IMU processing No smoothing will be performed This feature is very useful to compare forward and reverse attitude trajectories Run RTS smoother This option performs RTS back smoothing on the loosely coupled or tightly coupled solution Combine Setti
137. wse External button Regardless of which file is selected double check the File name field to ensure the proper file has been selected GNSS Variance factors for residuals Inertial Explorer performs residual testing using a standard least squares approach on position phase and Zero Velocity ZUPT updates Phase updates applied where there is a minimum of two satellites are only available in tightly coupled processing GNSS position updates and ZUPTs which are detected from raw IMU measurements can be applied in either loosely or tightly coupled processing Updates are accepted only if the computed residual is within the set tolerance The IMU processing profiles contain pre defined position variances for NovAtel SPAN models These have been tested to help ensure good results on typical surveys provided that lever arm has been accurately measured IMU gt GNSS lever arm accuracy is critical to post processing results as position velocity and phase updates measured at the GNSS antenna need to be applied at the IMU center of navigation The position variance should be greatly increased values of 50 to 100 if processing without accurately measured lever arms or if solving for them using the Solve lever arm values as additional Kalman filter states option described on Page 25 30 Inertial Explorer 8 20 User Guide Rev 6 Inertial Explorer Chapter 1 Extra GNSS Updates GrafNav uses Dopple
138. xed up Plot the vehicle GNSS derived Course over Ground vs the azimuth make sure your inertial defined heading has the right sense Otherwise Inertial Explorer simply processes your attitude data as is 4 7 How do I deal with unknown lever arm offsets from an IMU centre to a GNSS antenna It is important that the lever arm between the centre of the IMU and the GNSS LI phase centre be measured correctly in the field Otherwise the attitude information will not be optimal especially in heading This problem is particularly severe during turns Inertial Explorer 8 20 User Guide Rev 6 75 Chapter 4 FAQ and Tips However if this information is not available you can request that Inertial Explorer estimate the lever arm during data processing In such a case ensure that no Lever Arm Offset values are entered under the System tab of the IMU processing settings and that the Solver lever arm values as additional kalman filter states option is enabled In all likelihood the initial computed estimates are only accurate to the nearest 30 cm or 40 cm However you can refer to the FIM and RIM files for the lever arm estimates under the Lev field and enter them back into the System tab dialog box under Lever Arm Offset in a second iteration The processor now has better initial approximates to work with instead of just 0 0 s Iterate and re process until you have lever arm values which do not change significantly These mig

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