Java package/function that reads GPX files

John_Doe · June 30, 2022, 3:33am

Hello all,

I have added an element in my GPX file and would like this element to be available when doing map-matching. I have been looking at the JAVA source code but couldn’t figure out how this is done by GH.

I believe the function that creates GPX entries based on a file is the:

public static List<GPXEntry> createGPXList(InstructionList instructions)

inside the GpxConversions.java file. However, I can’t find the function that parses the GPX file itself.

Any help/suggestion is greatly appreciated.

EDIT: I’m a C++ developer and not very familiar with Java so please be kind.

easbar · June 30, 2022, 4:46am

Can you give an example of what you are trying to achieve?

The createGPXList method creates GPX entries based on the calculated route, not the (gpx input?) file.

John_Doe · June 30, 2022, 5:04am

Thank you for the response easbar.

I apologize if my post didn’t make sense.

I have an actual driven distance data for each GPS point and would like to replace the linearDistance:

final double linearDistance = distanceCalc.calcDist(prevTimeStep.observation.getPoint().lat, prevTimeStep.observation.getPoint().lon, timeStep.observation.getPoint().lat, timeStep.observation.getPoint().lon) + timeStep.observation.getAccumulatedLinearDistanceToPrevious();

for the:

double transitionLogProbability = probabilities.transitionLogProbability(path.getDistance(), linearDistance);

with the function similar to this:

final double drivenDistance = (timeStep.observation.getDrivenDistance() - prevTimeStep.observation.getDrivenDistance()) + timeStep.observation.getAccumulatedDrivenDistance();

then I can just use:

double transitionLogProbability = probabilities.transitionLogProbability(path.getDistance(), drivenDistance);

So I am thinking of adding this driven distance data in the GPX file in addition to the lon, lat and time (e.g. lon, lat, time and driven distance). I can then just read the GPX file and add the driven distance data in the observation class. However, I can’t seem to figure out how GH is reading input GPX files.

easbar · June 30, 2022, 5:27am

The code that reads the gpx file for the match command is here:

github.com

graphhopper/graphhopper/blob/fa1b12661fecf1e60974e490269aa618cadf63a4/web/src/main/java/com/graphhopper/application/cli/MatchCommand.java#L113

      
        
            StopWatch importSW = new StopWatch();
            StopWatch matchSW = new StopWatch();
            
            
Translation tr = new TranslationMap().doImport().getWithFallBack(Helper.getLocale(args.getString("instructions")));
            final boolean withRoute = !args.getString("instructions").isEmpty();
            XmlMapper xmlMapper = new XmlMapper();
            
            
for (File gpxFile : args.<File>getList("gpx")) {
                try {
                    importSW.start();
                    Gpx gpx = xmlMapper.readValue(gpxFile, Gpx.class);
                    if (gpx.trk == null) {
                        throw new IllegalArgumentException("No tracks found in GPX document. Are you using waypoints or routes instead?");
                    }
                    if (gpx.trk.size() > 1) {
                        throw new IllegalArgumentException("GPX documents with multiple tracks not supported yet.");
                    }
                    List<Observation> measurements = GpxConversions.getEntries(gpx.trk.get(0));
                    importSW.stop();
                    matchSW.start();
                    MatchResult mr = mapMatching.match(measurements);

So it is just XML deserialization and it should be easy to adjust the Gpx.java file so it includes a field for the property you like to add to the gpx file.

John_Doe · June 30, 2022, 5:44am

Exactly what I needed!

Thank you very much for your help.