Use the determinant formula for calculating the orientation of a polygon

server/src/main/java/org/elasticsearch/common/geo/builders/PolygonBuilder.java

@@ -642,14 +642,8 @@ private static int createEdges(int component, Orientation orientation, LineStrin
      */
     private static Edge[] ring(int component, boolean direction, boolean handedness,
                                  Coordinate[] points, int offset, Edge[] edges, int toffset, int length, final AtomicBoolean translated) {
-        // calculate the direction of the points:
-        // find the point a the top of the set and check its
-        // neighbors orientation. So direction is equivalent
-        // to clockwise/counterclockwise
-        final int top = top(points, offset, length);
-        final int prev = (offset + ((top + length - 1) % length));
-        final int next = (offset + ((top + 1) % length));
-        boolean orientation = points[offset + prev].x > points[offset + next].x;
+
+        boolean orientation = getOrientation(points, offset, length);
 
         // OGC requires shell as ccw (Right-Handedness) and holes as cw (Left-Handedness)
         // since GeoJSON doesn't specify (and doesn't need to) GEO core will assume OGC standards
@@ -678,6 +672,30 @@ private static Edge[] ring(int component, boolean direction, boolean handedness,
         return concat(component, direction ^ orientation, points, offset, edges, toffset, length);
     }
 
+    /**
+     * @return whether the points are clockwise (true) or anticlockwise (false)
+     */
+    private static boolean getOrientation(Coordinate[] points, int offset, int length) {
+        // calculate the direction of the points: find the southernmost point
+        // and check its neighbors orientation.
+
+        final int top = top(points, offset, length);
+        final int prev = (top + length - 1) % length;
+        final int next = (top + 1) % length;
+
+        // This duplicates the functionality of org.apache.lucene.geo.Polygon2D#orient which is, at time of writing, private.
+        // TODO make Lucene's method public and then use it here instead.
+        final double determinant
+            = (points[offset + next].x - points[offset + top].x) * (points[offset + prev].y - points[offset + top].y)
+            - (points[offset + prev].x - points[offset + top].x) * (points[offset + next].y - points[offset + top].y);
+        assert determinant != 0.0;
+        return determinant < 0.0;
+    }
+
+    /**
+     * @return the (offset) index of the point that is furthest west amongst
+     * those points that are the furthest south in the set.
+     */
     private static int top(Coordinate[] points, int offset, int length) {
         int top = 0; // we start at 1 here since top points to 0
         for (int i = 1; i < length; i++) {

server/src/test/java/org/elasticsearch/common/geo/builders/PolygonBuilderTests.java

@@ -143,4 +143,15 @@ public void testHoleThatIsNorthOfPolygon() {
 
         assertEquals("Hole lies outside shell at or near point (4.0, 3.0, NaN)", e.getMessage());
     }
+
+    public void testWidePolygonWithConfusingOrientation() {
+        // A valid polygon that is oriented correctly (anticlockwise) but which
+        // confounds a naive algorithm for determining its orientation leading
+        // ES to believe that it crosses the dateline and "fixing" it in a way
+        // that self-intersects.
+
+        PolygonBuilder pb = new PolygonBuilder(new CoordinatesBuilder()
+            .coordinate(10, -20).coordinate(100, 0).coordinate(-100, 0).coordinate(20, -45).coordinate(40, -60).close());
+        pb.build(); // Should not throw an exception
+    }
 }