a few fixes, added intersection and difference for collections

src/main/java/com/esri/core/geometry/OGCStructure.java

@@ -23,13 +23,8 @@
  */
 package com.esri.core.geometry;
 
-import java.util.ArrayList;
 import java.util.List;
 
-import com.esri.core.geometry.ogc.OGCConcreteGeometryCollection;
-import com.esri.core.geometry.ogc.OGCGeometry;
-import com.esri.core.geometry.ogc.OGCGeometryCollection;
-
 public class OGCStructure {
 	public int m_type;
 	public List<OGCStructure> m_structures;

src/main/java/com/esri/core/geometry/OGCStructureInternal.java

@@ -23,13 +23,6 @@
  */
 package com.esri.core.geometry;
 
-import java.util.ArrayList;
-import java.util.List;
-
-import com.esri.core.geometry.ogc.OGCConcreteGeometryCollection;
-import com.esri.core.geometry.ogc.OGCGeometry;
-import com.esri.core.geometry.ogc.OGCGeometryCollection;
-
 //An internal helper class. Do not use.
 public class OGCStructureInternal {
 	private static class EditShapeCursor extends GeometryCursor {

src/main/java/com/esri/core/geometry/ogc/OGCConcreteGeometryCollection.java

@@ -80,6 +80,11 @@ public OGCConcreteGeometryCollection(OGCGeometry geom, SpatialReference sr) {
 		esriSR = sr;
 	}
 
+	public OGCConcreteGeometryCollection(SpatialReference sr) {
+		geometries = new ArrayList<OGCGeometry>();
+		esriSR = sr;
+	}
+
 	@Override
 	public int dimension() {
 		int maxD = 0;
@@ -356,7 +361,7 @@ protected boolean isConcreteGeometryCollection() {
 		return true;
 	}
 
-	static class GeometryCursorOGC extends GeometryCursor {
+	private static class GeometryCursorOGC extends GeometryCursor {
 		private int m_index;
 		private int m_ind;
 		private List<OGCGeometry> m_geoms;
@@ -522,6 +527,9 @@ public int hashCode() {
 
 	@Override
 	public double distance(OGCGeometry another) {
+		if (this == another)
+			return isEmpty() ? Double.NaN : 0;
+
 		double minD = Double.NaN;
 		for (int i = 0, n = numGeometries(); i < n; ++i) {
 			double d = geometryN(i).distance(another);
@@ -535,6 +543,8 @@ public double distance(OGCGeometry another) {
 
 		return minD;
 	}
+
+	//
 	//Relational operations
 	@Override
 	public boolean disjoint(OGCGeometry another) {
@@ -569,7 +579,8 @@ public boolean disjoint(OGCGeometry another) {
 	@Override
 	public boolean contains(OGCGeometry another) {
 		if (isEmpty() || another.isEmpty())
-			return true;
+			return false;
+
 		if (this == another)
 			return false;
 
@@ -601,7 +612,79 @@ public boolean contains(OGCGeometry another) {
 		//each geometry of another is contained in a geometry from this.
 		return true;
 	}
-
+	//Topological
+	@Override
+	public OGCGeometry difference(OGCGeometry another) {
+		List<OGCConcreteGeometryCollection> list = wrapGeomsIntoList_(this, another);
+		list = prepare_for_ops_(list);
+		if (list.size() != 2) // this should not happen
+			throw new GeometryException("internal error");
+
+		List<OGCGeometry> result = new ArrayList<OGCGeometry>();
+		OGCConcreteGeometryCollection coll1 = list.get(0);
+		OGCConcreteGeometryCollection coll2 = list.get(1);
+		for (int i = 0, n = coll1.numGeometries(); i < n; ++i) {
+			OGCGeometry cur = coll1.geometryN(i);
+			for (int j = 0, n2 = coll2.numGeometries(); j < n2; ++j) {
+				OGCGeometry geom2 = coll2.geometryN(j);
+				if (cur.dimension() > geom2.dimension())
+					continue; //subtracting lower dimension has no effect.
+
+				cur = cur.difference(geom2);
+				if (cur.isEmpty())
+					break;
+			}
+
+			if (cur.isEmpty())
+				continue;
+
+			result.add(cur);
+		}
+
+		return new OGCConcreteGeometryCollection(result, esriSR);
+	}
+
+	@Override
+	public OGCGeometry intersection(OGCGeometry another) {
+		List<OGCConcreteGeometryCollection> list = wrapGeomsIntoList_(this, another);
+		list = prepare_for_ops_(list);
+		if (list.size() != 2) // this should not happen
+			throw new GeometryException("internal error");
+
+		List<OGCGeometry> result = new ArrayList<OGCGeometry>();
+		OGCConcreteGeometryCollection coll1 = list.get(0);
+		OGCConcreteGeometryCollection coll2 = list.get(1);
+		for (int i = 0, n = coll1.numGeometries(); i < n; ++i) {
+			OGCGeometry cur = coll1.geometryN(i);
+			for (int j = 0, n2 = coll2.numGeometries(); j < n2; ++j) {
+				OGCGeometry geom2 = coll2.geometryN(j);
+
+				OGCGeometry partialIntersection = cur.intersection(geom2);
+				if (partialIntersection.isEmpty())
+					continue;
+
+				result.add(partialIntersection);
+			}
+		}
+
+		return (new OGCConcreteGeometryCollection(result, esriSR)).flattenAndRemoveOverlaps();
+	}
+
+	//make a list of collections out of two geometries
+	private static List<OGCConcreteGeometryCollection> wrapGeomsIntoList_(OGCGeometry g1, OGCGeometry g2) {
+		List<OGCConcreteGeometryCollection> list = new ArrayList<OGCConcreteGeometryCollection>();
+		if (g1.geometryType() != OGCConcreteGeometryCollection.TYPE) {
+			g1 = new OGCConcreteGeometryCollection(g1, g1.getEsriSpatialReference());
+		}
+		if (g2.geometryType() != OGCConcreteGeometryCollection.TYPE) {
+			g2 = new OGCConcreteGeometryCollection(g2, g2.getEsriSpatialReference());
+		}
+
+		list.add((OGCConcreteGeometryCollection)g1);
+		list.add((OGCConcreteGeometryCollection)g2);
+
+		return list;
+	}
 	/**
 	 * Checks if collection is flattened.
 	 * @return True for the flattened collection. A flattened collection contains up to three non-empty geometries:
@@ -636,7 +719,7 @@ public boolean isFlattened() {
 	/**
 	 * Flattens Geometry Collection.
 	 * The result collection contains up to three geometries:
-	 * an OGCMultiPoint, an OGCMultiPolygon, and an OGCMultilineString.
+	 * an OGCMultiPoint, an OGCMultilineString, and an OGCMultiPolygon (in that order).
 	 * @return A flattened Geometry Collection, or self if already flattened.
 	 */
 	public OGCConcreteGeometryCollection flatten() {
@@ -804,17 +887,23 @@ private List<OGCConcreteGeometryCollection> prepare_for_ops_(List<OGCConcreteGeo
 		assert(geoms != null && !geoms.isEmpty());
 		GeometryCursor prepared = OGCStructureInternal.prepare_for_ops_(new FlatteningCollectionCursor(geoms), esriSR);
 
-		ArrayList<OGCConcreteGeometryCollection> result = new ArrayList<OGCConcreteGeometryCollection>();
+		List<OGCConcreteGeometryCollection> result = new ArrayList<OGCConcreteGeometryCollection>();
 		int prevCollectionIndex = -1;
-		ArrayList<Geometry> list = null;
+		List<Geometry> list = null;
 		for (Geometry g = prepared.next(); g != null; g = prepared.next()) {
 			int c = prepared.getGeometryID();
 			if (c != prevCollectionIndex) {
+				//add empty collections for all skipped indices
+				for (int i = prevCollectionIndex; i < c - 1; i++) {
+					result.add(new OGCConcreteGeometryCollection(esriSR));
+				}
+
 				if (list != null) {
 					result.add(removeOverlapsHelper_(list));
 				}
 
 				list = new ArrayList<Geometry>();
+				prevCollectionIndex = c;
 			}
 
 			list.add(g);

src/main/java/com/esri/core/geometry/ogc/OGCGeometry.java

@@ -253,7 +253,7 @@ public boolean isMeasured() {
 	 */
 	public boolean Equals(OGCGeometry another) {
 		if (this == another)
-			return true;
+			return true; //should return false for empty
 
 		if (another == null)
 			return false;
@@ -333,6 +333,9 @@ public boolean relate(OGCGeometry another, String matrix) {
 
 	// analysis
 	public double distance(OGCGeometry another) {
+		if (this == another)
+			return isEmpty() ? Double.NaN : 0;
+
 		if (another.geometryType() == OGCConcreteGeometryCollection.TYPE) {
 			return another.distance(this);
 		}
@@ -456,6 +459,10 @@ public OGCGeometry convexHull() {
 	}
 
 	public OGCGeometry intersection(OGCGeometry another) {
+		if (another.geometryType() == OGCConcreteGeometryCollection.TYPE) {
+			return (new OGCConcreteGeometryCollection(this, esriSR)).intersection(another);
+		}
+
 		com.esri.core.geometry.OperatorIntersection op = (OperatorIntersection) OperatorFactoryLocal
 				.getInstance().getOperator(Operator.Type.Intersection);
 		com.esri.core.geometry.GeometryCursor cursor = op.execute(
@@ -487,6 +494,10 @@ public OGCGeometry union(OGCGeometry another) {
 	}
 
 	public OGCGeometry difference(OGCGeometry another) {
+		if (another.geometryType() == OGCConcreteGeometryCollection.TYPE) {
+			return (new OGCConcreteGeometryCollection(this, esriSR)).difference(another);
+		}
+
 		com.esri.core.geometry.Geometry geom1 = getEsriGeometry();
 		com.esri.core.geometry.Geometry geom2 = another.getEsriGeometry();
 		return createFromEsriGeometry(

src/test/java/com/esri/core/geometry/TestOGC.java

@@ -983,6 +983,18 @@ public void testUnionGeometryCollectionWithGeometryCollection() {
 				"GEOMETRYCOLLECTION (POINT (3 5), LINESTRING (1 2, 2 3, 3 4, 5 6), POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0)))");
 	}
 
+	@Test
+	public void testIntersectionGeometryCollectionWithGeometryCollection() {
+		assertIntersection("GEOMETRYCOLLECTION (LINESTRING (1 2, 3 4), POLYGON ((0 0, 1 1, 0 1, 0 0)))", 
+				"GEOMETRYCOLLECTION (POINT (1 2), POINT (2 3), POINT (0.5 0.5), POINT (3 5), LINESTRING (3 4, 5 6), POLYGON ((0 0, 1 0, 1 1, 0 0)))",
+				"GEOMETRYCOLLECTION (MULTIPOINT ((1 2), (2 3), (3 4)), LINESTRING (0 0, 0.5 0.5, 1 1))");
+	}
+
+	private void assertIntersection(String leftWkt, String rightWkt, String expectedWkt) {
+		OGCGeometry intersection = OGCGeometry.fromText(leftWkt).intersection(OGCGeometry.fromText(rightWkt));
+		assertEquals(expectedWkt, intersection.asText());
+	}
+
 	private void assertUnion(String leftWkt, String rightWkt, String expectedWkt) {
 		OGCGeometry union = OGCGeometry.fromText(leftWkt).union(OGCGeometry.fromText(rightWkt));
 		assertEquals(expectedWkt, union.asText());