Add support for dateline wrapping for circle to geometry conversion (#…

…194)

* Circles that cross a dateline can now be converted to a JTS Geometry. Previous attempts would throw an exception. 
* JtsGeometry now supports input an Geometry that crosses the dateline multiple times (wraps the globe multiple times). Previous attempts would yield erroneous behavior.

Signed-off-by: Stijn Caerts <stijncaerts@gmail.com>

CHANGES.md

@@ -2,6 +2,12 @@
 
 DATE: _unreleased_
 
+* \#194: Circles that cross a dateline can now be converted to a JTS Geometry. Previous attempts would throw an exception. 
+ (Stijn Caerts)
+
+* \#194: JtsGeometry now supports input an Geometry that crosses the dateline multiple times (wraps the globe multiple times). Previous attempts would yield erroneous behavior.
+ (Stijn Caerts)
+
 * \#188: Upgraded to JTS 1.17.0.  This JTS release has a small [API change](https://github.com/locationtech/jts/blob/master/doc/JTS_Version_History.md#api-changes) and it requires Java 1.8.
   Spatial4J should work fine with older versions still.
   (Jim Hughes)

src/main/java/org/locationtech/spatial4j/shape/jts/JtsGeometry.java

@@ -573,11 +573,10 @@ private static Geometry cutUnwrappedGeomInto360(Geometry geom) {
       return geom;
     assert geom.isValid() : "geom";
 
-    //TODO opt: support geom's that start at negative pages --
-    // ... will avoid need to previously shift in unwrapDateline(geom).
     List<Geometry> geomList = new ArrayList<Geometry>();
     //page 0 is the standard -180 to 180 range
-    for (int page = 0; true; page++) {
+    int startPage = (int) Math.floor((geomEnv.getMinX() + 180) / 360);
+    for (int page = startPage; true; page++) {
       double minX = -180 + page * 360;
       if (geomEnv.getMaxX() <= minX)
         break;
@@ -586,7 +585,10 @@ private static Geometry cutUnwrappedGeomInto360(Geometry geom) {
       Geometry pageGeom = rect.intersection(geom);//JTS is doing some hard work
       assert pageGeom.isValid() : "pageGeom";
 
-      shiftGeomByX(pageGeom, page * -360);
+      if (page != 0) {
+        pageGeom = pageGeom.copy(); // because shiftGeomByX modifies the underlying coordinates shared by geom.
+        shiftGeomByX(pageGeom, page * -360);
+      }
       geomList.add(pageGeom);
     }
     return UnaryUnionOp.union(geomList);

src/main/java/org/locationtech/spatial4j/shape/jts/JtsShapeFactory.java

@@ -157,14 +157,16 @@ public Geometry getGeometryFrom(Shape shape) {
       //  http://docs.codehaus.org/display/GEOTDOC/01+How+to+Create+a+Geometry#01HowtoCreateaGeometry-CreatingaCircle
       //TODO This should ideally have a geodetic version
       Circle circle = (Circle)shape;
-      if (circle.getBoundingBox().getCrossesDateLine())
-        throw new IllegalArgumentException("Doesn't support dateline cross yet: "+circle);//TODO
       GeometricShapeFactory gsf = new GeometricShapeFactory(geometryFactory);
       gsf.setWidth(circle.getBoundingBox().getWidth());
       gsf.setHeight(circle.getBoundingBox().getHeight());
       gsf.setNumPoints(4*25);//multiple of 4 is best
       gsf.setCentre(new Coordinate(circle.getCenter().getX(), circle.getCenter().getY()));
-      return gsf.createCircle();
+      Geometry geom = gsf.createCircle();
+      if (circle.getBoundingBox().getCrossesDateLine())
+        // wrap the geometry in a JtsGeometry to handle date line wrapping
+        geom = new JtsGeometry(geom, (JtsSpatialContext) getSpatialContext(),false, false).getGeom();
+      return geom;
     }
     //TODO add BufferedLineString
     throw new InvalidShapeException("can't make Geometry from: " + shape);

src/test/java/org/locationtech/spatial4j/context/jts/JtsSpatialContextTest.java

@@ -13,6 +13,7 @@
 import org.locationtech.spatial4j.shape.jts.JtsGeometry;
 import org.locationtech.jts.geom.GeometryCollection;
 import org.locationtech.jts.geom.Polygon;
+import org.locationtech.jts.geom.MultiPolygon;
 import org.junit.Test;
 import org.locationtech.spatial4j.shape.jts.JtsShapeFactory;
 import org.locationtech.spatial4j.util.Geom;
@@ -62,4 +63,20 @@ public void testDatelineRuleWithMultiPolygon() {
                 "((0 0, 1 1, 1 0, 0 0))" +
                 ")", jtsGeometry.toString());
     }
+
+    @Test
+    public void testMultiDatelineWrap() {
+        // polygon crosses the dateline twice
+        Polygon polygon = Geom.build().points(-179, 45, 179, 44, 1, 35, -179, 25, 179, 24, 179, 19, -179, 20, 1, 30, 179, 39, -179, 40).toPolygon();
+
+        JtsSpatialContextFactory factory = new JtsSpatialContextFactory();
+        factory.datelineRule = DatelineRule.width180;
+        JtsSpatialContext ctx = factory.newSpatialContext();
+        JtsShapeFactory shapeFactory = ctx.getShapeFactory();
+        JtsGeometry jtsGeometry = shapeFactory.makeShape(polygon);
+        Geometry geometry = jtsGeometry.getGeom();
+
+        assertTrue(geometry.isValid());
+        assertTrue(geometry instanceof MultiPolygon);
+    }
 }

src/test/java/org/locationtech/spatial4j/shape/jts/JtsShapeFactoryTest.java

@@ -28,11 +28,13 @@
 import org.locationtech.spatial4j.context.jts.JtsSpatialContextFactory;
 import org.locationtech.spatial4j.distance.DistanceUtils;
 import org.locationtech.spatial4j.distance.GeodesicSphereDistCalc;
+import org.locationtech.spatial4j.shape.Circle;
 import org.locationtech.spatial4j.shape.Point;
 import org.locationtech.spatial4j.shape.Shape;
 import org.locationtech.spatial4j.shape.impl.GeoCircle;
 import org.locationtech.spatial4j.shape.impl.PointImpl;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
 public class JtsShapeFactoryTest {
@@ -94,7 +96,35 @@ private void circleGeometryConversionTest(double x, double y, double radiusKm) {
       Point point = new PointImpl(coordinate.x, coordinate.y, SpatialContext.GEO);
       double distance = distCalc.distance(point, circleCenter);
       double distanceKm = DistanceUtils.degrees2Dist(distance, DistanceUtils.EARTH_MEAN_RADIUS_KM);
-      Assert.assertEquals(String.format("Distance from point to center: %.2f km. Expected: %.2f km", distanceKm,
+      assertEquals(String.format("Distance from point to center: %.2f km. Expected: %.2f km", distanceKm,
+              radiusKm), radiusKm, distanceKm, maxDeltaKm);
+    }
+  }
+
+  @Test
+  public void testCircleDateLineWrapping() {
+    // left wrapping (-180)
+    circleGeometryConversionDateLineTest(-179.99, 51.22, 5);
+    // right wrapping (+180)
+    circleGeometryConversionDateLineTest(179.99, -35.6, 10);
+  }
+
+  private void circleGeometryConversionDateLineTest(double lon, double lat, double radiusKm) {
+    JtsShapeFactory shapeFactory = JtsSpatialContext.GEO.getShapeFactory();
+    Circle circle = shapeFactory.circle(lon, lat, DistanceUtils.dist2Degrees(radiusKm, DistanceUtils.EARTH_MEAN_RADIUS_KM));
+    Geometry geom = shapeFactory.getGeometryFrom(circle);
+
+    assertTrue(circle.getBoundingBox().getCrossesDateLine());
+    assertEquals("MultiPolygon", geom.getGeometryType());
+
+    GeodesicSphereDistCalc distCalc = new GeodesicSphereDistCalc.Haversine();
+    double maxDeltaKm = radiusKm / 100; // allow 1% inaccuracy
+    for (Coordinate c : geom.getCoordinates()) {
+      // Check distance from center of each point
+      Point point = new PointImpl(c.x, c.y, SpatialContext.GEO);
+      double distance = distCalc.distance(point, lon, lat);
+      double distanceKm = DistanceUtils.degrees2Dist(distance, DistanceUtils.EARTH_MEAN_RADIUS_KM);
+      assertEquals(String.format("Distance from point to center: %.2f km. Expected: %.2f km", distanceKm,
               radiusKm), radiusKm, distanceKm, maxDeltaKm);
     }
   }