TIP SHEET: Automatic Measurement of Triplet Offset
Contents
1. proceed to the List and click the button The Triplet Offset Points are now presented in the 3D Points List and 3D View Set iChange Units Remove scanned points Sounds Save as Default oF iY On Miscellaneous settings i Automatically backup project Files i Show thumbnail preview in tooltips i Show codes in the 30 view We Show cameras in the 30 view Show blue predicted points Reverse mouse wheel direction Scale options Scale via red retro reflective codes L Other OUrpUE Options EGO parameters Image coordinates Figure 2 Setting up the Triplet Targets To use triplet offset targets simply place any number of them within the scene of interest at the time of photography and iWitnessPRO will automatically measure them during the process Triplet offset points are shown in dark blue in the images and the 3D List and in red in the 3D View Each time a photogrammetric bundle adjustment is run the triplet offset points are recalculated in 3D and thus they are only temporary and not saved in the project file They can however be exported via the 3D points dialog for example in DXF format for consideration within third party CAD software Slide 3 Photograph the project with the camera settings described in Step 1 Figure 3 used a quantity of 12 coded targets and two scale bars along with 100 Triplet Offset Targets defining the curved geometry edges of the Table Top Note how the images are taken in a2. button lower middle of dialog box Note as soon as you accomplish this the Step 3 Generate DXF button will become active Click the button and save the DXF to your working folder Click Close The project is now complete Figure 12 amp 13 illustrate the results of the work in a CAD program A series of 3 Point ARCS were used to connect the 25 and the 15 Triplet Offset Targets NOTE one can also compress the Z axis to zero 0 in the iWitnessPRO DXF export options dialog box if the Triplets are being used on a planar surface XY Plane Witness Project Linking STEP 1 Import between 2 12 projects For linking Network one 11 TYE MASTER YYY Taple Top iwpra Network two 2 import Secondary iwpra Network three 3 Import Network Four 4 Import Network Five 5 Import Network six 64 Import Network seven 7 Import Network eight 91 Import Network nine 9 Import Network ten 10 Import Network eleven 114 Import Network twelve 12 Import Important TF you make a mistake just close amp reopen this dialog box gt 1 2 CPs 4 View Ps RMS 0 006 inches gt 9 10 10 11 Piet C 2D gt 30 Linking points prefix CP STEP 2 Perform linking PERERREEEE Slide 11 The Crash Zone 8 5 3 BOTH czd L File Edit Draw
3. ring pattern around the table top The camera was approximately 1 5 to 2 5 meters from the triplet targets 10 images were used but 20 were originally imaged It is always better to take more photos than less jWitnessPRO C PROJECTS Table Top Table Top 2 subset for demo Table Top iwpro Dw ht Ba BAS 3D Seliiiitiii it 2 so o 1 P1013745 JPG 2 P1013746 JPG E 5 P1013752 IPG 787768 SEB EZ Go sect mente RRIAT aaa g1 39 3g sed Ser Sr KET Table Top Active Photo 1 P1013745 JPG Slide 4 2a Follow the 2b Open one of the images and place the cursor within the image and see Figure 4 and button Click when complete to close out of the dialog box Image Scanning amp Auto Measurement settings Q key 4 P1013749 JPG Image scan tolerances left mouse click on image G Scanning threshold a H Min target width S Max target width d 100 Target IH ratio 3 0 Point measurement tolerances see manual for help Minimum pts Default points Maximum pts Triplet rank value 3 Intersection angle P Minimum no rays Driveback pixels a Figure 4 Slide 5 l l iWitnessPRO C PROJECTS Table Top Table Top subset for demo Table Top twpro Click the R fol lowed by the Beg n File Edit Photogrammetry irda Help Dae kt Be Be Apply Scale and follow the process described in Step 2 vi Auto refe
4. view Snaps Text Dimension Utilities ReconfAnimate 3D Window Help F1 D S td gt o 6 Z var S 22 wits FO Q QQQRHKRANM FO Quick Pick HIG DA m Je ME kefal o m EA ANANE Soe a Ma AG FT 1B d aK 00 RA R Quick Pick Z Draw Snap Hatch amp Line Types LS Edit fA Text Dimensions O view 3D 3D Tools Recon Animate O Symbols T Templates LS Forms 2 Learning Center W W e W W W W W W E Triplet Offset Targets were connected via the Crash Zone 3 Point ARC tool Figure 12 Slide 12 T The Crash Zone 8 5 3 BOTH czd File Edit Draw View Snaps Text Dimension Utilities ReconfAnimate 3D Window Help F1 1 Points 2 Labels 3 Description Slide 13 1 to coded targets or single feature points as they will function more consistently if left with some space approximately 1 diameter of the overall size surrounding them li Triplet offset targets from each other iii If a by iWitnessPRO it is possible to manually measure i e force it in the 3D view Select the three points that form the missed triplet and Letter O on the keyboard This will identify the triplet offset target and generate the offset point The three points forming the triplet offset target must have been calculated correctly for this to work iv If iWitnessPRO in a survey it may be useful to in the Image Scanning amp Auto Measurement settings dialog b
5. e the curve with more points NOTE the 12 coded targets and scale bars were not moved from the original survey and were also used in the second survey 25 Triplets e 15 Triplets r NAVO lt IIU VY C hem 5 Second Survey Figure 7 Slide 8 steps for the Second Survey 1 Remove enough of the 25 Triplets in the curved areas so the 15 Triplets can be applied adjacent to where the 25 Triplets were imaged noted in Figure 6 and 7 The camera settings are the same as Step 1 In Step 2 iii the Triplet Target Size needs to be changed from 25 to 15 Photograph the areas of the applied 15 triplets similar to Step 3 one needs to acquire at least 5 good overlapping perspective camera angle shots Figure 8 illustrates eight different camera observations on a randomly selected 15 Triplet Offset Target Complete the Step 4 work however there is No Need to Scale or 3 2 1 The only requirement is to name the CP points the same as Step 4 item 5 Save the project a different name e g Secondary IWDTO Figure 8 Slide 9 iWitnessPRO IEF Edit Photogrammetry Window Help Close out of the project assure there aren t any projects i e iwpro s minimized in the Windows task bar Click on the iWitnessPRO short cut and start a new project and select RSE Launch Zaraf File Import Projects for Linking see Figure 9 Prit P
6. efore rerunning a bundle adjustment It is also possible to though once again these are only temporary and it is important to note that running the bundle adjustment will remove lines between offset points Therefore and just prior to exporting a DXF file iWitnessPRO will give a warning message for the first line that is measured between offset points giving an option to force the bundle adjustment to be turned off to avoid accidentally removing lines between offset points see Figure 14 Similarly iWitness PRO will give a warning message before turning the bundle back on see Figure 15 A Bundle should be switched OFF to preserve lines between offset 2 points Switch it of now Figure 14 Slide 14
7. iWitnessPRO supports the use of triplet offset targets to facilitate automatic 3D measurement of untargetable features where it is difficult to accurately place a single red retro reflective target Such as the curved edges of a tabletop or a kitchen countertop The triplet offset target design is straightforward the tip of the triplet offset designates the point of interest as shown in Figure 1 EED POINT OF INTEREST Figure 1 This tip sheet illustrates the dialog boxes and user actions measuring the edges of a curved able Top In addition to measuring with the 25 dot triplet offset targets a secondary network was also accomplished illustrating how one might use both 25 and 15 Triplet Offset Targets in the same project For more information on Triplet Offset Targets visit Section D3 of the iWitnessPRO User Manual 2010 All Rights Reserved DeChant Consulting Services DCS Inc amp Photometrix www iwitnessphoto com Slide 1 Working with Triplet Offset Targets o We recommend using a DSLR Camera with settings as follows 1 2 3 4 Manual set on the dial and also using Shutter Speed 1 125 of a second Aperture about F13 the goal is to UNDEREXPOSE the images a couple F stops ISO 400 the Triplet Targets and codes must be illuminated by the flash f your camera to target distance is only a few meters away then we recommend the following 6a Temporarily put the camera
8. in autofocus 6b Depress the shutter button half way down this will focus the lens making the triplets sharply focused 6c With the camera still on use the camera as described in step 1 through 5 if the Triplet targets are in a camera to target range of 2m to say 6m simply set the ALWAYS shoot the this is required for the camera s self calibration see Part C Section C2 of the User Manual for more information In the dialog Edit Project Settings the Tick Mark for Triplet Offset Targets must be selected to ensure iWitnessPRO automatically measures triplet offset targets Refer to Figure 2 for the proper settings Note the tick mark for the 25 Target configuration e You can optionally open up the shutter to about F8 to allow more light to manually measure Natural Features as well This tip sheet was designed for the optimum exposure of Triplet Offset Targets thus the reason the imagery appears dark or underexposed Slide 2 i Red Targets must be selected li Find triplet offset targets must be selected lil The physical size of the targets on the triplet offset targets must be selected either 0 15 or 0 25 iV for an iWitnessPRO network before the triplet offset feature will function correctly Optionally scale via retro reflective codes can be selected in the Project Settings dialog We recommend scaling using scale bars l Once the Right Click Set Scale
9. release Triplets are illustrated in Figure 5 Different sizes of triplet offset targets within the same bundle adjustment i e project but the size of the triplet offset targets can be different to the size of the coded targets via the Project Settings dialog The small sized triplet offset targets are useful when there is a lot of detail to be measured in a small area and the medium sized triplet offset targets are useful for normal scenes BLACK BACKGROUND 0 15 RED TARGETS r 0 225 0 375 0 500 0 325 Dimensions of 0 15 Triplet Offset Targets small Figure 5 BLACK BACKGROUND 0 25 RED TARGETS 0 750 1 000 0 625 Dimensions of 0 25 Triplet Offset Targets medium Slide 7 Secondary objective of the Demo Project including the 15 triplet offset targets Background The demo project incorporated curves on the 4 corners of the Table Top Figure 6 In this initial project the 25 dot Triplets are physically too large to try and place enough of them to define the curves as noted in the areas of the red arrows in Figure 6 To better define the curves a quantity of 11 15 Triplet Offset Targets were survey independently subsequent to the initial survey of which originally used the 25 Triplets Figure 7 illustrates where a quantity of 3 of the 25 Triplets were removed after the original survey with another quantity of 3 of the 15 Triplets placed in a second survey to better defin
10. rence Right Mouse Click and apply the 3 2 1 Note we named the 4 points that were measured from 2 scale bars as CP1 CP2 CP3 and CP4 with the 3 2 1 conducted using CP1 as the origin CP2 as the point to define the axis and CP3 as the point to fall on plane See section B4 of the User Manual for more information on the 3 2 1 process Referencing progress Images Scanned Stations Solved Lines can now optionally be connected as noted in Step 3 Points Referenced iWitnessPRO C PROJECTS Table Top T File Edit Photogrammetry Window Help Ose ht i RR To export click on the 3D List DUOn c g7 so E and click DXF export and save the DXF file Ea Aae Bundle RMS microns for later use in a CAD program Fy Bundle Iteration i Find new points This completes the process a s PSE J egin steps Now let s look at a z cc s PE ae ae rm Continue optionally adding some gt S Ts aT CE of the smaller 15 dot Triplets g a ve o in the following slides s The CP naming convention is required for Project Linking used later on in this tip sheet Slide 6 There are currently two different sizes of triplet offset targets available small and medium Small triplet offset targets have 0 15 3 8mm targets overall length 1 425 36 2mm and medium triplet offset targets have 0 25 6 35mm targets overall length 2 875 73 0mm A larger Triplet will be available in a future
11. rint Preview 1 mini trilpet run The Project Linking dialog is now displayed see Figure 10 2 CHPROIECTS Table Top 3 subset of 10 images S Taple Top Te 9 Click the Import button as indicated in Figure 10 NOTE the project Network one 1 you import will be the initial project accomplished For this tip iWitness Project Linking Network one 1 MASTER Import Click for the noted Step 9 sheet we named the initial project Table Top iwpro Network two 2 Click the Import button as indicated in Figure 10 arz NOTE the project Network two 2 you import havent four will be the second project accomplished For Te this tip sheet we named the second project ar Network six 6 Secondary iwpro bert H Network seven 7 Figure 11 illustrates the coordinate transformation result R The Table Top iwpro and the Secondary iwpro are now o in the same coordinate system ready to export as a DXF Ee file toO a third party CAD program Network ten 10 gt 9 10 Import i Network eleven 11 gt 10 11 Network twelve 12 K 11 12 Import C 2D 3D Linking points prefix CP Fic JU re 1 0 i Slide 10 Note the RMS 006 fit in the upper right With precision scaling a decent consumer grade DSLR camera and a good self calibration this result is typical of a project the size of the demo example networks 11 Click the
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