"Invalid ordinate index: 2" When reducing polygon precision

[lesingh]

We upgraded from JTS 1.16.0 to 1.18.2 and now the following code:

GeometryPrecisionReducer reducer = new GeometryPrecisionReducer(new PrecisionModel(Math.pow(10, 12)));
reducer.reduce(geometry);

...gives the following error...

java.lang.IllegalArgumentException: Invalid ordinate index: 2
	at org.locationtech.jts.geom.CoordinateXY.setOrdinate(CoordinateXY.java:131)
	at org.locationtech.jts.geom.impl.CoordinateArraySequence.setOrdinate(CoordinateArraySequence.java:304)
	at org.locationtech.jts.operation.overlayng.ElevationModel$2.filter(ElevationModel.java:217)
	at org.locationtech.jts.geom.LineString.apply(LineString.java:244)
	at org.locationtech.jts.geom.Polygon.apply(Polygon.java:310)
	at org.locationtech.jts.operation.overlayng.ElevationModel.populateZ(ElevationModel.java:202)
	at org.locationtech.jts.operation.overlayng.OverlayNG.getResult(OverlayNG.java:488)
	at org.locationtech.jts.operation.overlayng.PrecisionReducer.reducePrecision(PrecisionReducer.java:62)
	at org.locationtech.jts.precision.PrecisionReducerTransformer.reduceArea(PrecisionReducerTransformer.java:120)
	at org.locationtech.jts.precision.PrecisionReducerTransformer.transformPolygon(PrecisionReducerTransformer.java:112)
	at org.locationtech.jts.geom.util.GeometryTransformer.transform(GeometryTransformer.java:129)
	at org.locationtech.jts.precision.PrecisionReducerTransformer.reduce(PrecisionReducerTransformer.java:41)
	at org.locationtech.jts.precision.GeometryPrecisionReducer.reduce(GeometryPrecisionReducer.java:156)

Any ideas what could be causing this? It looks like it's looking for Z values in a 2D polygon? Is there something I need to set? geometry.getDimension() returns 2.

[dr-jts]

It's possible this is a bug. Can you provide a reproducer in code?

[lesingh]

So, it looks like we had two 2D polygons. Then we called intersect to create a 3rd polygon. The third polygon is reportedly two dimensional, but it actually has some z points in it.

reduce() fails because it doesn't like the mixed 2D and 3D coordinates.

import org.locationtech.jts.geom.*;
import org.locationtech.jts.precision.*;

public class Test {
        public static void main(String[] args) {
                Coordinate[] coord = new Coordinate[4];
                coord[0] = new Coordinate(-96.2188040642255,40.8825518351343,0);
                coord[1] = new CoordinateXY(-96.237792969, 40.783813477);
                coord[2] = new CoordinateXY(-96.250297546, 40.783813477);
                coord[3] = new Coordinate(-96.2188040642255,40.8825518351343,0);
                PrecisionModel pModel = new PrecisionModel(Math.pow(10, 12));
                GeometryFactory factory = new GeometryFactory();
                Polygon polygon = factory.createPolygon(coord);
                GeometryPrecisionReducer reducer = new GeometryPrecisionReducer(pModel);
                reducer.reduce(polygon);
        }
}

This code snippet doesn't replicated the behavior of intersection() where 2 polygons are passed in and outputs mixed coordinates. I still need to look into that.

[lesingh]

Bear with me, but when I was testing, I noticed that intersected polygons don't always return the same type of coordinates. For example:

import org.locationtech.jts.geom.*;

public class Test {
        public static void main(String[] args) {
                Coordinate[] coord2 = new Coordinate[5];

                coord2[0] = new CoordinateXY(-1.00001,3.00001);
                coord2[1] = new CoordinateXY(1.00001,3.00001);
                coord2[2] = new CoordinateXY(1.00001,-3.00001);
                coord2[3] = new CoordinateXY(-1.00001,-3.00001);
                coord2[4] = new CoordinateXY(-1.00001,3.00001);

                Polygon p2 = factory.createPolygon(coord2);

                Geometry[] geoArray = {p2};
                GeometryCollection geomCollection = new GeometryCollection(geoArray,factory);
                Geometry p3 = geomCollection.intersection(p2);
                System.out.println("Points: " + p3.toText()); //Shows points
                for(Coordinate c : p3.getCoordinates()) {
                        System.out.println(c.getClass()+ " " + c.toString() + ", "); //Mixed Coordinate and CoordinateXY
                }
        }
}

Is mixed 2d and 3d points intentional? This doesn't cause an error when calling reduce(), because the Z-axis is NaN. But I'm pretty sure there is one case where Z ends up as 0, instead of NaN, in our code, which does cause a problem when reduce() is called. I'm just having difficulty reproducing it.

Anyway, I'll continue investigating.

[dr-jts]

That is probably a bug. The handling of coordinate dimensions is complex and still imperfect, unfortunately.

[lesingh]

I was able to get past the last error by flattening my GeometryCollection using a CoordinateOperation and replacing all instances of Coordinate with CoordinateXY.

But, then I ran into a new error:

Exception in thread "main" java.lang.IllegalArgumentException: Reduction failed, possible invalid input
	at org.locationtech.jts.operation.overlayng.PrecisionReducer.reducePrecision(PrecisionReducer.java:66)
	at org.locationtech.jts.precision.PrecisionReducerTransformer.reduceArea(PrecisionReducerTransformer.java:120)
	at org.locationtech.jts.precision.PrecisionReducerTransformer.transformPolygon(PrecisionReducerTransformer.java:112)
	at org.locationtech.jts.geom.util.GeometryTransformer.transform(GeometryTransformer.java:129)
	at org.locationtech.jts.geom.util.GeometryTransformer.transformGeometryCollection(GeometryTransformer.java:300)
	at org.locationtech.jts.geom.util.GeometryTransformer.transform(GeometryTransformer.java:133)
	at org.locationtech.jts.precision.PrecisionReducerTransformer.reduce(PrecisionReducerTransformer.java:41)
	at org.locationtech.jts.precision.GeometryPrecisionReducer.reduce(GeometryPrecisionReducer.java:156)

This exception doesn't tell me much, because the original exception gets eaten up by the try/catch in PrecisionReducer.java at line 66.

But after debugging some more, I was able to get entire stack trace of the failure:

        TopologyException "unable to assign free hole to a shell"
        PolygonBuilder.placeFreeHoles(List<OverlayEdgeRing>, List<OverlayEdgeRing>) line: 185	
	PolygonBuilder.buildRings(List<OverlayEdge>) line: 64	
	PolygonBuilder.<init>(List<OverlayEdge>, GeometryFactory, boolean) line: 37	
	PolygonBuilder.<init>(List<OverlayEdge>, GeometryFactory) line: 31	
	OverlayNG.extractResult(int, OverlayGraph) line: 581	
	OverlayNG.computeEdgeOverlay() line: 509	
	OverlayNG.getResult() line: 483	
	PrecisionReducer.reducePrecision(Geometry, PrecisionModel) line: 62	
	PrecisionReducerTransformer.reduceArea(Geometry) line: 120	
	PrecisionReducerTransformer.transformPolygon(Polygon, Geometry) line: 112	
	PrecisionReducerTransformer(GeometryTransformer).transform(Geometry) line: 129	
	PrecisionReducerTransformer(GeometryTransformer).transformGeometryCollection(GeometryCollection, Geometry) line: 300	
	PrecisionReducerTransformer(GeometryTransformer).transform(Geometry) line: 133	
	PrecisionReducerTransformer.reduce(Geometry, PrecisionModel, boolean) line: 41	
	GeometryPrecisionReducer.reduce(Geometry) line: 156	

Apparently, when OverlayNG initializes PolygonBuilder, it assumes the geometry is polygonal for some reason, and then fails when the geometry is not polygonal. Is there a reason for restricting Geometry objects to be polygonal when calling reduce?

I used a GeometryCollection in my code, but I see the error still happens when just using a Polygon. See below:

               Coordinate[] coord = new Coordinate[5];

                coord[0] = new CoordinateXY(-96.903694153, 40.523513794);
                coord[1] = new CoordinateXY(-96.893592834, 40.52351379400002);
                coord[2] = new CoordinateXY(-96.874893188, 40.52341079699999);
                coord[3] = new CoordinateXY(-96.893592835, 40.52351379400002);
                coord[4] = new CoordinateXY(-96.903694153, 40.523513794);

                PrecisionModel pModel = new PrecisionModel(Math.pow(10, 12));
                GeometryFactory factory = new GeometryFactory();
                Polygon poly = factory.createPolygon(coord);
                GeometryPrecisionReducer reducer = new GeometryPrecisionReducer(pModel);
                reducer.reduce(poly);