Check whether a route self intersects

Asked Dec 19 '18 at 14:22

Active Dec 19 '18 at 15:07

Viewed 119 times

I have numerous routes, each defined by its many points which in turn are defined by their corresponding Gcs coordinates (latitude,longitude). I was trying to find an efficient Java implementation to determine which lines are self-intersecting and I was referred to JTS.

This is what I was trying to do:

public boolean intersects(List<GcsNode> nodes) {

       Coordinate[] sequence = new Coordinate[route.size()];
       for (int i = 0; i < nodes.size(); i++) {
           sequence[i] = toCartesian(nodes.get(i).latitude(), nodes.get(i).longitude());
       }

       GeometryFactory factory = new GeometryFactory();
       return !factory.createLineString(sequence).isSimple();

}

public static final double DIST = 6371.0;


public Coordinate toCartesian(double latitude, double longitude) {

       return new Coordinate(DIST * Math.cos(latitude) * Math.cos(longitude),
                DIST * Math.cos(latitude) * Math.sin(longitude));
}

Unfortunately, the intersects method always returns true, no matter if the routes are self-intersecting or not. Does anybody know what I am doing wrong?

edited Dec 19 '18 at 15:07

asked Dec 19 '18 at 14:22

João Matos

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Are your `latitude` and `longitude` in degrees or radians? – Andy Turner Dec 19 '18 at 14:27
@AndyTurner they are in degrees. – João Matos Dec 19 '18 at 14:29
2

Does `Math.cos` and `Math.sin` need the angles in degrees or radians? (I'm not saying this is the fix for your problem; merely that this is a bug in the code). – Andy Turner Dec 19 '18 at 14:30
Radians, thanks for the help – João Matos Dec 19 '18 at 14:33
I guess Math.toRadians() should solve my problem – João Matos Dec 19 '18 at 14:39
It is still not working @AndyTurner, The code probably has two problems.. – João Matos Dec 19 '18 at 14:48
Shouldn't you be returning `! ... isSimple()` to detect intersection? – Andy Turner Dec 19 '18 at 14:50
I am already doing so, sorry for the typo - edited – João Matos Dec 19 '18 at 14:52
If you really want to work in metres instead of degrees you should reproject to a local coordinate system - see [this answer](https://stackoverflow.com/questions/44249945/how-to-use-geometricshapefactory-in-geotools-to-create-a-circle-on-map/44256659#44256659) for a pointer on how to do it using JTS and GeoTools – Ian Turton Dec 19 '18 at 16:38
also check the line you get out is valid and !simple – Ian Turton Dec 19 '18 at 16:39
not sure, would need to look at the actual values going in – Ian Turton Dec 19 '18 at 17:13

Check whether a route self intersects

0 Answers0