report - Distributed Computing Group
Contents
1. wr gt EN Ta e g 7 EN TL xs Ze WO Oe S mis AN Sh PAR 7 Sieh 7 Figure 2 3 Overlay of a sampled route and the map CHAPTER 2 GPS Map sPs Meters Above Sealevel Sample Figure 2 4 Height correlation between map and GPS H Satellites HDOP 1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 Sample Figure 2 5 Road trip through villages CHAPTER 2 GPS 60 50 40 Satellites HDOP 30 20 O HA 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 Sample Figure 2 6 Walking through the forest 25 20 Satellites HDOP ooo oot T a 34048 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 Sample Figure 2 7 Running back through the forest Chapter 3 The Java Programs 3 1 GPS API The API that parses the NMEA0183 sentences mentioned in 2 1 1 was the core part of my thesis First of all I had to get the data through the serial port of the iPAQ from the GPS receiver into my Java program The corresponding API Java Com munications API was defined but not implemented for the PocketPC So 1 used an implementation written by James Nord 10 in order to communicate with the GPS rec2. Appendix A Contents of the CD ROM Additional Software This folder contains a copy of the Jeode JVM a copy of the Java Communications API and of the patched Thinlet library These tools have to be installed prior to using the GPS software GPS API The core part of the software described in Chapter 3 1 GPS Javadoc The Java documentation for the GPS API GPS Map Application described in Chapter 3 2 4 GPS Painter Application described in Chapter 3 2 2 GPS SwissParser A little tool that produces a summary of gathered GPS data see README file for details GPS Tracer Application described in Chapter 3 2 1 GPS Visualizer Application described in Chapter 3 2 3 25 APPENDIX A CONTENTS OF THE CD ROM INSTALL txt This file contains installation instructions for all the software provided There is a README in each application directory with a closer description 26
3. Defense Official Website http www defenselink mil GPS A New Constellation Exhibition Home Page http www nasm si edu exhibitions gps Global Positioning System Overview http www colorado edu geography geraft notes gps gps_f html The National Marine Electronics Association http www nmea org HAiCOM GPS http www haicom com tw HAiCOM GPS Support http www haicom com tw support htm Formeln und Konstanten fuer die Berechnung der Schweizerischen schiefachsigen Zylinderprojektion und der Transformation zwischen Koordinatensystemen http www swisstopo ch data geo refsysd pdf Page 11 Nicolas Burri Semester Thesis Java on the iPAQ Summer 2003 http dceg ethz ch theses ss03 ipaq_report pdf Java Communications API Pocket PC WinCE Driver http www teilo net software CEJavaComm Thinlet Website http www thinlet com Thinlet Tutorials http thinlet blog city com read 643909 htm Thinlet Paint Patch http uk geocities com mike_hartshorn2 Thinlet_paintpatch java JIMI Software Development Kit http java sun com products jimi 23 BIBLIOGRAPHY 24 15 16 17 How to Write Doc Comments for the Javadoc Tool http java sun com j2se javadoc writingdoccomments nSonic Software PocketSnap http nsonic de software pocketpc pocketsnap pocketsnap htm Net Compact Framework http www microsoft com downloads details aspx FamilyID 359ea6da fc5d 41cc ac04 7bb50a134556 amp displaylang en
4. JAVA PROGRAMS 11 In addition to this it is possible to flush a certain amount of characters onto the standard output with the function flushData int The Javadoc to this API is available at 1 3 1 1 GPS Tools Some tools that might be useful but do not directly belong to the GPS API can be found in the class GPS_Tools It includes public Sats getAllSatsFromGSV which provides complete information about the visible satellites in a structured way public String nmeaLines int which returns the specified number of NMEA0183 sentences as a string and finally a method to find out which ports are available in the system called public String listAvailablePorts 3 2 Java Applications A further task of my thesis was to design and implement a sample application that is based on the API written in the first part Instead of one large applications I wrote a few smaller ones that use various kinds of information provided by the GPS system I decided to do the GUI with Thinlet 11 as it is relatively easy to learn and based on pure AWT which is fast enough for the PocketPC One of the main advantages of Thinlet is that you can describe your GUI in XML and without having knowledge about AWT although it might be possible that there is a more efficient way to implement the GUI part directly with AWT It would be possible to use Swing as well but referring to 9 it seems to be too slow and you need some tricks to get it running I implemented three
5. UTC Coordinated Universal Time latitude longitude altitude and the current dilution of precision The GSA sentence gives information about the satellites that are currently used for the determination of the position All visible satellites then are listed in the GSV sentence and the RMC gives a kind of summary including UTC and date latitude longitude speed and course This is the most interesting information for everyday life 2 2 Accuracy and Reliability of the GPS Receiver 2 2 1 Accuracy Position Height and Speed According to the manufacturer of the GPS receiver HAiCOM we should be able to determine where we are within a radius of 10m in 95 of the cases For the velocity they specify an accuracy of 0 1 meters per second 0 36km h The time should be within 1 microsecond synchronized to the GPS time In addition to this I did my own tests I drove and walked around taking samples in constant intervals The GPS receiver indicates the accuracy in terms of Horizontal Dilution of Precision HDOP Position Dilution of Precision PDOP Vertical Dilution of Precision VDOP DOP is a mathematical representation for the quality of the GPS position solution The lower these values are the better is the accuracy the optimum is 1 The following three sections present results Position The accuracy highly depends on how many satellites are visible and how they are distributed The wider the satellite distribution and the more sat
6. display them in an appropriate manner on an iPAQ de vice In particular I used a Compaq iPAQ 3870 PDA portable digital assistant in combination with a HAiCOM GPS receiver 6 I started parsing the data from the GPS receiver After that my task was to develop some applications that operate on the GPS API written in the first step and in the end to determine how accurate and reliable this system is The applications should display as well as trace the position information in an appropriate way All of the software is written in Java since it is then possible to run the same pro gram not only on the iPAQ but on any system with a serial port e g PCMCIA or CompactFlash interface for the HAiCOM GPS receiver to fit in and a Java Virtual Machine JVM version 1 1 or higher The two disadvantages of this approach were the slightly limited JVM available for PDAs and the loss in speed that comes with its additional abstraction layer Chapter 2 GPS The system was originally developed by the U S Department of Defense 2 for mili tary purposes only Until May 2000 timing errors were inserted to limit the accuracy to 100 200m Without this so called selective availability it is now possible to deter mine your position within a range of less than 10m if enough satellites are available There are at least 24 operating satellites that orbit the earth in 12 hours Their constellation is such that from any point on earth you should be able to get signals
7. from usually five to eight satellites at a time A line of sight between the receiver and the satellite is required in order to use it Peter H Dana 9 22 98 GPS Nominal Constellation 24 Satellites in 6 Orbital Planes 4 Satellites in each Plane 20 200 km Altitudes 55 Degree Inclination Figure 2 1 GPS Constellation For more information about GPS see 3 and 4 CHAPTER 2 GPS 4 2 1 HAiCOM GPS Receiver For this thesis I used a GPS receiver by HAiCOM 6 It is mainly a CompactFlash extension card that comes with an adapter for the PCMCIA interface and therefore is treated as a serial interface in Java The iPAQ had to be equipped with a PCMCIA jacket for this purpose The receiver comes without much software All I had was a small application to test whether the device was working and to determine the correct COM port for it The GPS information is given in the NMEA v2 2 format also known as NMEA0183 The receiver produces an updated version of each part of the NMEA0183 protocol every second For detailed specifications see 7 2 1 1 NMEA 0183 NMEA stands for National Marine Electronics Association 5 and consists of a stan dardized set of giving info sentences from which I used the following GGA Global Positioning System Fix Data GSA GPS Dilution of Precision and Active Satellites GSV GPS Satellites in View RMC Recommended Minimum Specific GPS Data The most important fields of the GGA sentence are the
8. programs designed for the iPAQ and one to visualize the stored GPS information on a desktop computer see sections below All of them operate based on the model view controller pattern and are fully multi threaded There is always a class containing the main function which is responsible for showing the GUI and starting stopping the threads Their job is to keep updating the GUI with current information 3 2 1 GPS Tracer This application allows the user to see the GPS information in a human readable version It consists of a few tabs containing various kinds of information about the current position Figure 3 1 the satellites that are currently used Figure 3 2 the dilution of precision the tracking mode etc Furthermore it is possible to watch the NMEA0183 sentences unaltered as soon as they are received Figure 3 3 A last part provides the possibility to do a tracing over a time period That allows the user to store all the gathered position samples into an XML file The user can choose what should be stored limited to the information contained in the GGA sentence and in what interval the samples should be taken Figure 3 4 This interval is limited to 2 seconds because it takes about 1 second to parse the appropriate sentence and the sentence is only received once a second While tracing it is possible to watch the change of the altitude in an online chart Figure 3 5 CHAPTER 3 THE JAVA PROGRAMS GPS Tracer E m Tracing n
9. Semester Thesis GPS on iPAQ Philip Frey freyp student ethz ch Dept of Computer Science Swiss Federal Institute of Technology ETH Zurich Prof Dr Roger Wattenhofer Distributed Computing Group Supervisor Aaron Zollinger Winter 2004 05 Contents 1 Introduction 2 2 GPS 3 2 1 HAiCOM GPS Receiver o aaa 4 2121 NMEA 0183802 ot fad ba dt A eee a 4 2 2 Accuracy and Reliability of the GPS Receiver 4 2 2 1 Accuracy Position Height and Speed 4 2 2 2 Reliability Evaluation in Everyday Situations 6 3 The Java Programs 10 Sr HGP A ahaha ote cick Ya ee cian ey denice ORO 10 SLL GPS Slools 2 4 de Gee a a e eee ede E 11 3 2 JavacApplications s s 44 6 fe a ace eA Ele Goh RR 11 O2 GPS Tracer wn Sa do oa eee ee ee ls 11 32 2 GPS Painter anc oo o Ee a s To eh ha 14 S23 GPRS Visualizer aaa See Gace tee Gk ty gd a i A 14 3 24 GPS Ma Ds a a a eh Pee ALA c e ae ee Se ck eee 16 3 3 Work Progress and Difficulties ee ee ie eis 16 4 Conclusion 18 A ab ded be de bese oh gS Anda ds din dite oo Obed A 18 dde UNCC tt as eth ti as ol e 18 ALB GPS AA bt EES EO Re ah ah a EAS at a ed 18 5 Useful Hints 19 A Contents of the CD ROM 25 Chapter 1 Introduction One of the most commonly used positioning systems today is the Global Positioning System GPS The goal of this semester thesis is to acquire information from this system and save as well as
10. Tracking Latitude Longitude Speed o knots o ri GPS Tracer Ei m Pos Sat_NMEA Tracing att GPS Tracer E m x Pos Sat_NMEA Tracing Alt GPGSA A 3 11 14 03 19 GPGGA 135548 983 4714 8 GPRMC 135547 983 4 4714 GPGSA A 3 11 14 03 19 GPGGA 135547 983 4714 8 GPRMC 135546 983 4 4714 GPGSV 2 2 08 11 28 272 3 GPGSV 2 1 08 19 79 285 3 GPGSA A 3 11 14 03 19 4 EF GPS Tracer Figure 3 3 NMEA sentences 12 CHAPTER 3 THE JAVA PROGRAMS 13 GPS Tracer a m x Pos Sat NMEA Tracing alt Tracing pan GPS Tracer Figure 3 4 Recording GPS information GPS Tracer E m pos Sat mea Tracing ait Figure 3 5 Altitude graph CHAPTER 3 THE JAVA PROGRAMS 14 GPS Painter Control Settings Info EH GPS Painter Figure 3 6 Painted route 3 2 2 GPS Painter The GPS painter was originally called Human Pen The idea is that the user becomes a pen on the world and the application paints his movements in real time onto the iPAQ display Figure 3 6 Once the user has finished his her journey it can be saved into an XML file similar to the one from the GPS Tracer Figure 3 7 There are only minor differences between the two XML files To view the trace sometime later this XML file can be imported again the program can be run in Simulator mode so it will not use the real GPS data but the ones from the XML file specified Figure 3 8 It is possi
11. as recommended in 9 and had no problems at all running the programs on the iPAQ So download JDK 1 1 8 and unpack it somewhere into your system e g C jdk1 1 8 For the next step start Eclipse and set the JRE as well as the corresponding compiler Go to Window gt Preferences gt Java gt Installed JREs and add the jdk1 1 8 or whatever you are using then go to Compiler choose the tab Compliance and Classfiles and set the Generated class files compatibility to 1 1 How to access a device through the serial port of the iPAQ First of all you need to install the Java Communications API on the iPAQ as follows 1 Download the archive from http www teilo net 2 Copy CESerial jar comm jar and javax comm properties into a new folder 19 CHAPTER 5 USEFUL HINTS 20 on the iPAQ e g windows Java and commapi d11 into windows This driver for the serial port is free for non commercial use Now you can access the serial port as described in 10 There is some sample code which shows the recommended way of doing it Your link to start the java application on the iPAQ using the serial interface has to contain the Java Communications API in the classpath 80 Windows evm exe cp windows Java comm jar windows Java CESerial jar MyClass Where to get the exact specifications for the NMEA0183 sentences from the HAiCOM GPS receiver http www haicom com tw support htm How to test the GPS receiver I used the little t
12. ble to set some options that will improve the way the current trace is displayed Figure 3 8 These options include a zoom factor the origin on the screen the sampling interval and some visual options draw sample points and connections between them The zoom factor goes from 1 to 100 where the first reveals more details and the latter gives an overview of the journey When 1 is used one pixel corresponds approximately to one meter where with 100 one pixel corresponds to one kilometer These are just estimates to give an idea about the dimension A summary of the current settings is available in the Info menu The most difficult part of this application was to be able to paint directly on the GUI through its graphics context I had to use a patched version of Thinlet because the original one did not support painting at that time The patched version offers the possibility to define a paint method that is called whenever it is needed The method repaint allows a manual invocation of the paint function see Chapter 5 for details 3 2 3 GPS Visualizer In order to display the gathered data from the GPS Tracer as well as from the GPS Painter on a desktop computer with larger capacity I wrote the GPS Visualizer This tool has some additional features but is still based on the GPS Painter For example specific colors for the background or the trace etc can be set or an image can be exported as a JPG or PNG file This operation takes t
13. e always stored in the root directory of the iPAQ How to create image files with Java 1 1 Since this feature is not yet supported you have to use something like Jimi 14 It is very limited and slow due to the restricted resources of the iPAQ How to paint into the graphics context of the Thinlet GUI This feature is not contained in the stable release yet So you have to patch the thinlet jar file 1 Unpack the thinlet jar archive jar xf thinlet jar 2 Replace the file Thinlet java with the one from 13 rename it to Thinlet java and build the jar file again jar cf thinlet jar Now you have an additional attribute for every component called paint myPaintMethod where you can specify a method that is called whenever a repaint of that spe cific component is needed It needs to have the following signature public void lYou can omit the MANIFEST INF CHAPTER 5 USEFUL HINTS 22 myPaintMethod Thinlet t Object component Graphics g int width int height Therein you can redraw the component e g with g drawLine fromX fromY toX toY How to take screenshots on the iPAQ There is a small freeware tool called PocketSnap available at 16 On older devices it might be necessary to install the NET Compact Framework first It is free as well and available for download at 17 Bibliography 10 11 12 13 14 GPS on iPAQ Website http bosco ath cx gps U S Department of
14. eiver The next step was to parse the NMEA0183 sentences Each sentence begins with a followed by some numbers separated by commas and ends with lt CR gt lt LF gt For the exact meanings of the numbers in the different sentences see the User Manual Chapter Output Protocol at 7 I decided to use for each sentence an individual class in Java to store the current GPS information Here is an example of how to use the GPS API GPS gps new GPS COM5 RMC rmc new RMC try gps updateRMC rmc catch Exception e oP 02 b2 Fe Line 1 initializes the GPS API on COM Line 2 creates a new RMC object and Line 4 updates the RMC Object with the current GPS values It is not possible to open the GPS API more than once otherwise an Exception will be thrown All the information included in an RMC sentence can be accessed as member variables of the rmc object In order to get the current latitude rmc lat would for instance be used All the Java classes contain exactly the same information as the corresponding NMEA0183 sentences The only exception is the RMC class where I have added a function getSpeedKMHO to get the current speed in terms of km h instead of knots It is also possible to get the unparsed InputStream handle for the byte stream of the GPS receiver from the GPS API For that purpose I have provided the following two functions public InputStream startGPS public void stopGPS 10 CHAPTER 3 THE
15. ellites are visible CHAPTER 2 GPS 5 the more accurate is the position information The absolute position accuracy equals the dilution of precision times the measurement precision So if the measurement precision is 1m and the PDOP is 5 then the best position accuracy we can hope for is 5m The maps in Switzerland are subdivided by a grid with cells of 1 km each I used that grid to estimate the accuracy of the device in the following way First I located a number of points on the map then I drove there and sampled the latitude and longitude values at these points The next step was to determine the mean values of the samples and transform them into Swiss coordinates according to 8 Now I could calculate the deviation see Figure 2 2 These figures are not very precise though in fact it is not much more accurate than 5m An overlay of a sampled route and the map shows a similar picture see Figure 2 3 Deviation m X Deviation 2 1 3 8 6 3 2 3 4 2 1 10 4 1 7 2 2 6 Y Deviation 2 2 3 12 5 5 9 6 13 2 6 13 13 2 8 8 3 4 Figure 2 2 GPS position deviation from map coordinates Height In order to determine how accurate the height data is I decided to visit points that are marked on the map with exact heights I used the Landeskarte der Schweiz Blatt 1112 Ausgabe 1998 1 25000 for that purpose The height indicated by the GPS module does not correspond with the height marked on the swiss map It has to be t
16. figures 2 5 2 7 The minimum required number of satellites to determine the current position is three four for the additional height information A direct line of sight to the satellite is required Road On the road I almost never had less than three satellites and the average number was around 6 It attracts attention that there are some peak values in the DOP curve They correspond always to the loss of at least one satellite The opposite direction is not necessarily true though The figures in the city Zurich were similar I therefore do not present them here Forest The walk through the forest shows a similar picture Figure 2 4 I started the sam pling outside the forest walked about 15min through a small canyon covered with trees and ended up on a hill above it The average number of satellites used was around 4 still enough to calculate the current position On my way back down I ran Figure 2 7 In this third chart it is remarkable that the average DOP value is much higher than in the other ones It consists almost only of peaks although the aver age number of satellites was not much lower around 3 5 The reason for the peaks is that we are close to the critical amount of the necessary three or four satellites respectively CHAPTER 2 GPS CIR TUY AL A J A Ps EN S A Ps a ES ON SUD YAE NEES YD WA 7 NA al a gt de lt A 7 L gt x sz ES eo ig NOU AG A
17. hinlet see Page 21 It should be available in the next standard version as well Nevertheless I would rather use AWT directly for a next thesis So you do not depend on a feature to be implemented but you are able to use the whole AWT API as such It would be really bad if there was an important feature missing which was fortunately not the case during my work 4 3 GPS The GPS system needs a direct line of sight to the satellites in order to work This results in some overhead during the testing phase The programs have to be tested outdoors It takes about one or two minutes every time the GPS has to reinitialize before it produces the first valid set of data In order to circumvent this outside testing overhead I wrote the simulator which is available in the GPS Painter 18 Chapter 5 Useful Hints As it was pretty tough to start in such an unfamiliar environment I would like to give some hints here how to do the most basic things with Java and the iPAQ PocketPC Some very helpful tips and tricks concerning the installation of the JVM on the iPAQ the basics of Jeode and debugging can be found in 9 Where to find some more information about Jeode Some very useful information about Jeode can be found in the semester thesis by Nicolas Burri 9 and on the following website http www cs unc edu lindsey 7ds notes jeode How to set up Eclipse with the correct compiler for Jeode Throughout the project I I worked with Java 1 1 8
18. oo long on the GPS CHAPTER 3 THE JAVA PROGRAMS 15 GPS Painter Save current trace as an xml file Filename xmi FG GPS Painter Figure 3 7 Save journey in XML GPS Painter s Zoom dBorigo Interval V Draw Samples Vv Draw Lines v Simulator J GPS Painter Figure 3 8 Available settings activated simulator CHAPTER 3 THE JAVA PROGRAMS 16 Figure 3 9 GPS Map iPAQ since Java 1 1 does not support these image export functions directly I tried to solve this problem with a tool by Sun called Jimi 14 but the PocketPC was not fast enough It took about one minute to produce the output of a trace with only a few dozen samples and the size of the image was restricted to about 800x800 pixels I consequently decided to implement this functionality on the PC only 3 2 4 GPS Map What would GPS be without a map So I implemented another variant of the GPS Painter this time with segments of the Swiss map in the background Figure 3 9 The little red crosses indicate the visited positions The map has been divided into segments of 1km each If you leave one part of the map the application switches to the next one and so forth The trace will be saved so that if you return into a previous part your old position samples will be still there It is also possible so switch between different map segments manually Figure 3 10 In this tool the user is offered the possibili
19. ool called GPS Info available at the HAiCOM website mentioned above The serial port settings for the GPS receiver Baudrate 4800 Data bit 8 Parity None Stop bit 1 Flow control None How to create Javadoc from source files In your code you have to use the following syntax to create Javadoc contents in your source code my Javadoc comment At the end you can export these comments as Javadoc by choosing File gt Export gt Javadoc and specifying the source files you want to include For more details see 15 CHAPTER 5 USEFUL HINTS 21 How to create a Thinlet GUI The idea behind Thinlet 11 is to specify the look and feel of an AWT GUI in an external file that is parsed whenever the program is executed There are lots of easy to use components called widgets you can use to build up your GUI In your Java code the controller you have to import that XML description and initialize a new Thinlet object see example below For details please refer to 11 A very small example can be found at 12 Java example import thinlet public class MyClass extends Thinlet public MyClass throws Exception add parse description xml public static void main String args throws Exception new FrameLauncher MyClass new MyClass 320 240 FOOANOOORNEF 0 I cannot find the file I have just created with my Java application If you do not specify the whole path the files ar
20. ransformed first according to 8 The deviation in Figure 2 4 is within a range of 11m Even if more than four satellites are available the accuracy does not get much better So the height is the least accurate information In tendency the GPS values are a few meters above the map values Speed To measure the speed I went to a long straight part of a motorway There I took the distance information that is marked every 200m along the road and determined the distance I drove and measured the time needed for that With that information CHAPTER 2 GPS 6 I could calculate the approximate speed Then I compared this speed to the speed of the car I was using taking into account the error of the car s speed indicator which I got from a car magazine The combination of these two methods allowed me to determine my actual speed at an accuracy of about 1km h It was not possible though to verify the specified 0 36km h accuracy but 1 could verify that it is within lkm h Presumably this is enough for all practical purposes 2 2 2 Reliability Evaluation in Everyday Situations To determine the reliability of the device I chose two typical situations for the em ployment of the GPS system The first one of them was a road trip that started at the harbor led me through some smaller villages and over interurban roads The second one was a walk through a canyon in the forest As a measure I used the number of available satellites as well as the DOP see
21. t is very well documented with some samples a good start for anyone who needs a GUI and does not want to or cannot follow the common approach The disadvantage of Thinlet showed up when it came to the real time plot I had to use a patched version of it in order to be able to draw into the GUI using its graphics context see also Chapter 5 Chapter 4 Conclusion 4 1 Jeode One of the most popular advantages about Java is its platform independency This thesis gave me a good opportunity to test it Once I had written an application for Jeode the Java Virtual Machine running on the iPAQ there was no problem running the same application on the notebook as well The other way round is not necessarly true though On the laptop I wrote the applications for Java 1 4 2 whereas Jeode is based on the older Java 1 1 with a reduced function set There are a lot of things not available on Java 1 1 when it comes to graphics This increased the work a lot by things that should be available by default these days 4 2 Thinlet Thinlet offers a simple way to create nice looking AWT GUIs with almost every functionaliConclusionty The idea of Thinlet is that the user specifies the look of the GUI in an XML file This will then be parsed at runtime and the corresponding AWT GUI will be created I didn t miss anything except the possibility to paint directly in the GUIs graphics context Fortunately this feature can be added by using the patched version of T
22. ty to save his journey into an XML file in the same way as in the GPS Painter The accuracy is on average between five and ten meters In the program there are currently 56km of the city of Zurich available but it is very easy to add more segments as long as they follow the predescribed rules In order to work with the hard coded program settings the map segments must be parts of 1km xlkm each and scaled to 234x234 pixels The upper left corner of the square kilometer rectangle has to be 10 pixels off the top and left border The square kilometer rectangle itself must be 200x200pixels The code could also be easily adapted to meet different map specifications 3 3 Work Progress and Difficulties The first difficult thing was to find out how the Jeode JVM can communicate with the GPS receiver I browsed the web and found the solution at http www teilo net see Chapter 5 for details The parsing of the NMEA frames was not too tricky anymore after having read the exact specifications of the standard although it took me a while Then I had to look for a possibility to design the GUI since I have never CHAPTER 3 THE JAVA PROGRAMS 17 GPS Map Control Move Settings Info e North NOE a ry A South DS 4 Se FOC gt Eat K 14V NY o os ONS f a Figure 3 10 Switch between different map segments done that before There are some valid alternatives to the pure AWT SWT or Swing I can recommend Thinlet since i
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