Casting LineString to Polygon results in ClassCastException when y coordinates are the same

Question

final WKTReader wktReader = new WKTReader();
String geomString = "MULTILINESTRING ((-98.753985 34.63093, -98.7555568 34.63093))";
MultiLineString geom = (MultiLineString)wktReader.read(geomString);
LineString newGeom = new GeometryFactory().createLineString(geom.getCoordinates());
Polygon envelope = (Polygon) newGeom.getEnvelope();

Such code results with ClassCastException(). However, when I'm changing y value of any of coordinates, e.g. first one to 34.63094, I don't get any error.
I am using org.locationtech.jts-1.17.

What would I like to achieve is to cast it to Polygon without this Exception. Or, the exception is actually valid and I shouldn't be able to cast any two-coordinate LineString to Polygon?

Answer 1

Because your MultiLineString is a vertical line JTS gives you back a line when you ask for the envelope (it thinks this is helpful). So you need to ask for the internalEnvelope which will give you an Envelope (an xmin/xmax, ymin/ymax). You can then convert this into a Polygon using the org.geotools.geometry.jts.JTS Utility class.

final WKTReader wktReader = new WKTReader();
String geomString = "MULTILINESTRING ((-98.753985 34.63093, -98.7555568 34.63093))";
MultiLineString geom = (MultiLineString) wktReader.read(geomString);
LineString newGeom = new GeometryFactory().createLineString(geom.getCoordinates());
Geometry envelope = newGeom.getEnvelope();
System.out.println(envelope);
Envelope env = newGeom.getEnvelopeInternal();
System.out.println(env);
Polygon polygon = JTS.toGeometry(env);
System.out.println(polygon);

Which produces:

LINESTRING (-98.7555568 34.63093, -98.753985 34.63093)
Env[-98.7555568 : -98.753985, 34.63093 : 34.63093]
POLYGON ((-98.7555568 34.63093, -98.753985 34.63093, -98.753985 34.63093, -98.7555568 34.63093, -98.7555568 34.63093))

Note: the polygon will still look like a line as it has no width, but I guess that is what you want.