GeoTools JTS orthodromicDistance throws exception for latitude being out of range

Question

I am trying to get geotools to tell me the distance between two points. I am providing the points in degrees, and I want to get back the distance in meters. I followed this web page for instruction:

http://docs.geotools.org/stable/userguide/library/api/jts.html

Unfortunately when I run it, an exception is thrown because it says my latitude is out of range.

Here is my code:

public double measureDistanceInMeters(double[] coord1, double[] coord2) {
    System.out.println("latitude: "+coord1[0]+", longitude: "+coord1[1]);
    System.out.println("latitude: "+coord2[0]+", longitude: "+coord2[1]);
    CoordinateReferenceSystem crs = DefaultGeocentricCRS.CARTESIAN;
    // latitude first, longitude second.
    Coordinate start = new Coordinate(coord1[0],coord1[1]);
    Coordinate end = new Coordinate(coord2[0],coord2[1]);
    double distance = -1;
    try {
        distance = JTS.orthodromicDistance(start, end, crs);
    } catch (TransformException e1) {
        e1.printStackTrace();
    }
    return distance;

When I run it, the console prints this:

latitude: 38.8951, longitude: -77.0367
latitude: 40.7127, longitude: -74.0059

JUnit fails and here is the stack trace:

java.lang.IllegalArgumentException: Latitude �N is out of range (±90°).
    at org.geotools.referencing.GeodeticCalculator.checkLatitude(GeodeticCalculator.java:389)
    at org.geotools.referencing.GeodeticCalculator.setStartingGeographicPoint(GeodeticCalculator.java:550)
    at org.geotools.referencing.GeodeticCalculator.setStartingPosition(GeodeticCalculator.java:591)
    at org.geotools.geometry.jts.JTS.orthodromicDistance(JTS.java:635)
    at fungle.funfinder.data.geo.GeoToolsRuler.measureDistanceInMeters(GeoToolsRuler.java:49)
    at fungle.funfinder.data.geo.GeoRulerBase.getDistance(GeoRulerBase.java:15)
    at fungle.funfinder.data.geo.GeoToolsRulerTest.test(GeoToolsRulerTest.java:11)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

So I think I am misunderstanding something here. Geotools is huge, and even though it has documentation, it's pretty hard to find the documentation you're looking for because it's so huge and complicated.

I am guessing that I am using the wrong coordinate reference system here, or passing as an arg where I should not be. I don't know what I'm doing wrong. Please help.

Answer 1

You are using the wrong coordinate system, essentially you have told JTS that your coordinates need to be converted to lat/long and then used so they go out of range.

By changing your code to include:

    CoordinateReferenceSystem crs = null;
    try {
        crs = CRS.decode("epsg:4326");
    } catch (NoSuchAuthorityCodeException e) {
        e.printStackTrace();
    } catch (FactoryException e) {
        e.printStackTrace();
    }

I get the answer 328739.66 m or 328Km which sounds about right (if it isn't then you may need to swap the latitude and longitude values round).

You will also need to add

    <dependency>
        <groupId>org.geotools</groupId>
        <artifactId>gt-epsg-hsql</artifactId>
        <version>${geotools.version}</version>
    </dependency>

to your pom.xml file or the definition of the coordinate system won't be found.