Read M value (CoordinateXYZM) from shapefile with geotools

Question

After successfully writing M values into a shapefile (.shp, only points for now), I now also want to read the generated file and print the full coordinate set (x, y, z and m) using geotools (23-SNAPSHOT).

I found two different ways to do it (see code below) but both only give me a normal Coordinate object that has an M attribute, which is always NaN. I know that writing the file was successful because QGIS can see the full coordinates (including M).

How do I read the file, while still getting the actual M values?

Code I've tested:

1.From official website:

File f = new File(path);
Map<String, Object> map = new HashMap<String, Object>();

try {
    map.put("url", f.toURI().toURL());
    DataStore dataStore = DataStoreFinder.getDataStore(map);
    String typeName = dataStore.getTypeNames()[0];

    FeatureSource<SimpleFeatureType, SimpleFeature> source = dataStore.getFeatureSource(typeName);
    Filter filter = Filter.INCLUDE; // ECQL.toFilter("BBOX(THE_GEOM, 10,20,30,40)")    
    FeatureCollection<SimpleFeatureType, SimpleFeature> collection = source.getFeatures(filter);
    FeatureIterator<SimpleFeature> features = collection.features();

    while(features.hasNext()) {
        SimpleFeature feature = features.next();
        List attributes = feature.getAttributes();
        Collection properties = feature.getProperties();

        if(attributes.get(0) instanceof Point) {
            Point p = (Point) attributes.get(0);
            Coordinate c = p.getCoordinate(); //"c.getM()" returns "NaN"
            CoordinateXYZM cxyzm = new CoordinateXYZM(c); //"cxyzm.getM()" returns "0.0"
        }
    }
} catch (Exception e) {
    System.out.println("Exception: "+e);
}

2.From a question here on Stackexchange:

File f = new File(path);

try {
    FileDataStore store = FileDataStoreFinder.getDataStore(f);
    SimpleFeatureSource featureSource = store.getFeatureSource();
    SimpleFeatureCollection featureCollection = featureSource.getFeatures();
    SimpleFeatureIterator it = featureCollection.features();

    while(it.hasNext()){
        SimpleFeature feat = it.next();
        Geometry g = (Geometry) feat.getDefaultGeometry(); //"org.locationtech.jts.geom.Geometry", NOT "org.opengis.geometry.Geometry"!
        Coordinate c = g.getCoordinate(); //"c.getM()" returns "NaN"
        CoordinateXYZM cxyzm = new CoordinateXYZM(c); //"cxyzm.getM()" returns "0.0"
    }
} catch (IOException e) {
    System.out.println("Exception: "+e);
}

Answer 1

From a quick look at the ShapeFile reading code it appears that GeoTools just reads the M value and throws it away. So it looks like what you are trying to do is impossible.

I haven't tested it but if you change line 89 to

cs.setOrdinate(0, CoordinateSequence.M,  buffer.getDouble());

it should work. If you test this and it does work please make a PR for future users.