OGCGeometry union method does not behave as expected

[aaron-zonder-meer]

It seems that the union method on the OGCGeometry does not behave as expected. The first case is when a MultiPolygon with multiple inner rings is unioned with itself. The second case is when a MultiPolygon with multiple inner rings is unioned with a simple polygon (rectangle).

The set up is as follows:

version:

<dependency>
    <groupId>com.esri.geometry</groupId>
    <artifactId>esri-geometry-api</artifactId>
    <version>2.2.4</version>
</dependency>

example code snippet:

    public String unionSameShape() {
        OGCGeometry geom1 = createGeom2();
        OGCGeometry geom2 = createGeom2();

        return geom1.union(geom2).asGeoJson();
    }

    public String unionDifferentShapes() {
        OGCGeometry geom1 = createGeom1();
        OGCGeometry geom2 = createGeom2();

        return geom1.union(geom2).asGeoJson();
    }

    private OGCGeometry createGeom1() {
        return OGCGeometry.fromGeoJson(
                "{\"type\": \"Polygon\",\n" +
                        "        \"coordinates\": [\n" +
                        "          [\n" +
                        "            [\n" +
                        "              -15.599122,\n" +
                        "              -1.933227\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              18.640097,\n" +
                        "              -1.933227\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              18.640097,\n" +
                        "              2.504085\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              -15.599122,\n" +
                        "              2.504085\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              -15.599122,\n" +
                        "              -1.933227\n" +
                        "            ]\n" +
                        "          ]\n" +
                        "        ]\n" +
                        "      }");
    }

    private OGCGeometry createGeom2() {
        return OGCGeometry.fromGeoJson(
                "{\"type\": \"MultiPolygon\",\n" +
                        "        \"coordinates\": [\n" +
                        "          [\n" +
                        "            [\n" +
                        "              [\n" +
                        "                -10,\n" +
                        "                -10\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                10,\n" +
                        "                -10\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                10,\n" +
                        "                10\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -10,\n" +
                        "                10\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -10,\n" +
                        "                -10\n" +
                        "              ]\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              [\n" +
                        "                -4,\n" +
                        "                -4\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -4,\n" +
                        "                4\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                4,\n" +
                        "                4\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                4,\n" +
                        "                -4\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -4,\n" +
                        "                -4\n" +
                        "              ]\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              [\n" +
                        "                -5,\n" +
                        "                -5\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -5,\n" +
                        "                5\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                5,\n" +
                        "                5\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                5,\n" +
                        "                -5\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -5,\n" +
                        "                -5\n" +
                        "              ]\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              [\n" +
                        "                -7,\n" +
                        "                -7\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -7,\n" +
                        "                7\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                7,\n" +
                        "                7\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                7,\n" +
                        "                -7\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -7,\n" +
                        "                -7\n" +
                        "              ]\n" +
                        "            ],\n" +
                        "            [\n" +
                        "              [\n" +
                        "                -6,\n" +
                        "                -6\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -6,\n" +
                        "                6\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                6,\n" +
                        "                6\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                6,\n" +
                        "                -6\n" +
                        "              ],\n" +
                        "              [\n" +
                        "                -6,\n" +
                        "                -6\n" +
                        "              ]\n" +
                        "            ]\n" +
                        "          ]\n" +
                        "        ]\n" +
                        "      },\n" +
                        "      \"id\": \"11c45056-3ee0-4e56-993e-22da21bbff69");
    }

Result union on same shape:

{
   "type":"MultiPolygon",
   "coordinates":[
      [
         [
            [
               -10,
               -10
            ],
            [
               10,
               -10
            ],
            [
               10,
               10
            ],
            [
               -10,
               10
            ],
            [
               -10,
               -10
            ]
         ],
         [
            [
               -7,
               -7
            ],
            [
               -7,
               7
            ],
            [
               7,
               7
            ],
            [
               7,
               -7
            ],
            [
               -7,
               -7
            ]
         ]
      ],
      [
         [
            [
               -6,
               -6
            ],
            [
               6,
               -6
            ],
            [
               6,
               6
            ],
            [
               -6,
               6
            ],
            [
               -6,
               -6
            ]
         ]
      ]
   ],
   "crs":null
}

result of union with different shape:

{
   "type":"MultiPolygon",
   "coordinates":[
      [
         [
            [
               -10,
               -10
            ],
            [
               10,
               -10
            ],
            [
               10,
               -1.933227000000001
            ],
            [
               18.640097,
               -1.933227
            ],
            [
               18.640097,
               2.504085
            ],
            [
               10,
               2.5040849999999995
            ],
            [
               10,
               10
            ],
            [
               -10,
               10
            ],
            [
               -10,
               2.504085
            ],
            [
               -15.599122,
               2.504085
            ],
            [
               -15.599122,
               -1.933227
            ],
            [
               -10.000000000000002,
               -1.9332269999999994
            ],
            [
               -10,
               -10
            ]
         ],
         [
            [
               -7,
               -7
            ],
            [
               -7.000000000000001,
               -1.9332269999999996
            ],
            [
               -6,
               -1.9332269999999991
            ],
            [
               -6,
               2.5040849999999995
            ],
            [
               -7,
               2.5040849999999995
            ],
            [
               -7,
               7
            ],
            [
               7,
               7
            ],
            [
               7,
               2.504084999999999
            ],
            [
               6,
               2.504084999999999
            ],
            [
               6,
               -1.9332270000000005
            ],
            [
               7,
               -1.9332270000000005
            ],
            [
               7,
               -7
            ],
            [
               -7,
               -7
            ]
         ]
      ],
      [
         [
            [
               -6,
               -6
            ],
            [
               6,
               -6
            ],
            [
               6,
               -1.9332270000000005
            ],
            [
               5,
               -1.9332270000000005
            ],
            [
               5,
               2.504084999999999
            ],
            [
               6,
               2.504084999999999
            ],
            [
               6,
               6
            ],
            [
               -6,
               6
            ],
            [
               -6,
               2.5040849999999995
            ],
            [
               -5,
               2.5040849999999995
            ],
            [
               -5,
               -1.933226999999999
            ],
            [
               -6,
               -1.9332269999999991
            ],
            [
               -6,
               -6
            ]
         ]
      ]
   ],
   "crs":null
}

original shapes:

[alocke]

Hi Aaron, I will take a look.

[stolstov]

@aaron-zonder-meer I believe the problem here is because the second multipolygon seems to be invalid. It consists of a single Polygon that consists of 5 concentric rings. Instead, it should consist of 3 polygons, and the holes should be oriented according to the spec: See this https://tools.ietf.org/html/rfc7946#section-3.1.6 https://tools.ietf.org/html/rfc7946#section-3.1.7

Try using makeSimple on the second geometry before passing it to union.

[aaron-zonder-meer]

@stolstov Thank you very much for your quick response. Like you said, this geometry was not according to the spec, and not considered 'simple' in the framework. Your solution helped a great deal. As far as I'm concerned, this issue can be closed.