[turf] Add turf area measurement method.

CHANGELOG.md

@@ -4,6 +4,8 @@ Mapbox welcomes participation and contributions from everyone.
 
 ### master
 
+- Added support for Turf area measurement method [#1079](https://github.com/mapbox/mapbox-java/pull/1079)
+
 ### 4.9.0 - September 23, 2019
 - Added intersection search support to MapboxGeocoding [#1074](https://github.com/mapbox/mapbox-java/pull/1074)
 - Added support for Turf polygonToLine method [#1075](https://github.com/mapbox/mapbox-java/pull/1075)

docs/turf-port.md

@@ -8,7 +8,7 @@ Below's an on going list of the Turf functions which currently exist inside the
 
 ## Measurement
 - [x] turf-along
-- [ ] turf-area
+- [x] turf-area
 - [x] turf-bbox
 - [x] turf-bbox-polygon
 - [x] turf-bearing

services-turf/src/main/java/com/mapbox/turf/TurfMeasurement.java

@@ -39,6 +39,11 @@ private TurfMeasurement() {
     throw new AssertionError("No Instances.");
   }
 
+  /**
+   * Earth's radius in meters.
+   */
+  public static double EARTH_RADIUS = 6378137;
+
   /**
    * Takes two {@link Point}s and finds the geographic bearing between them.
    *
@@ -572,4 +577,123 @@ public static BoundingBox square(@NonNull BoundingBox boundingBox) {
       );
     }
   }
+
+  /**
+   * Takes one {@link Feature} and returns it's area in square meters.
+   *
+   * @param feature input {@link Feature}
+   * @return area in square meters
+   * @since 4.10.0
+   */
+  public static double area(@NonNull Feature feature) {
+    return feature.geometry() != null ? area(feature.geometry()) : 0.0f;
+  }
+
+  /**
+   * Takes one {@link FeatureCollection} and returns it's area in square meters.
+   *
+   * @param featureCollection input {@link FeatureCollection}
+   * @return area in square meters
+   * @since 4.10.0
+   */
+  public static double area(@NonNull FeatureCollection featureCollection) {
+    List<Feature> features = featureCollection.features();
+    double total = 0.0f;
+    if (features != null) {
+      for (Feature feature : features) {
+        total += area(feature);
+      }
+    }
+    return total;
+  }
+
+  /**
+   * Takes one {@link Geometry} and returns it's area in square meters.
+   *
+   * @param geometry input {@link Geometry}
+   * @return area in square meters
+   * @since 4.10.0
+   */
+  public static double area(@NonNull Geometry geometry) {
+    return calculateArea(geometry);
+  }
+
+  private static double calculateArea(@NonNull Geometry geometry) {
+    double total = 0.0f;
+    if (geometry instanceof Polygon) {
+      return polygonArea(((Polygon) geometry).coordinates());
+    } else if (geometry instanceof MultiPolygon) {
+      List<List<List<Point>>> coordinates = ((MultiPolygon) geometry).coordinates();
+      for (int i = 0; i < coordinates.size(); i++) {
+        total += polygonArea(coordinates.get(i));
+      }
+      return total;
+    } else {
+      // Area should be 0 for case Point, MultiPoint, LineString and MultiLineString
+      return 0.0f;
+    }
+  }
+
+  private static double polygonArea(@NonNull List<List<Point>> coordinates) {
+    double total = 0.0f;
+    if (coordinates.size() > 0) {
+      total += Math.abs(ringArea(coordinates.get(0)));
+      for (int i = 1; i < coordinates.size(); i++) {
+        total -= Math.abs(ringArea(coordinates.get(i)));
+      }
+    }
+    return total;
+  }
+
+  /**
+   * Calculate the approximate area of the polygon were it projected onto the earth.
+   * Note that this area will be positive if ring is oriented clockwise, otherwise
+   * it will be negative.
+   *
+   * Reference:
+   * Robert. G. Chamberlain and William H. Duquette, "Some Algorithms for Polygons on a Sphere",
+   * JPL Publication 07-03, Jet Propulsion
+   * Laboratory, Pasadena, CA, June 2007 https://trs.jpl.nasa.gov/handle/2014/41271
+   *
+   * @param coordinates  A list of {@link Point} of Ring Coordinates
+   * @return The approximate signed geodesic area of the polygon in square meters.
+   */
+  private static double ringArea(@NonNull List<Point> coordinates) {
+    Point p1;
+    Point p2;
+    Point p3;
+    int lowerIndex;
+    int middleIndex;
+    int upperIndex;
+    double total = 0.0f;
+    final int coordsLength = coordinates.size();
+
+    if (coordsLength > 2) {
+      for (int i = 0; i < coordsLength; i++) {
+        if (i == coordsLength - 2) { // i = N-2
+          lowerIndex = coordsLength - 2;
+          middleIndex = coordsLength - 1;
+          upperIndex = 0;
+        } else if (i == coordsLength - 1) { // i = N-1
+          lowerIndex = coordsLength - 1;
+          middleIndex = 0;
+          upperIndex = 1;
+        } else { // i = 0 to N-3
+          lowerIndex = i;
+          middleIndex = i + 1;
+          upperIndex = i + 2;
+        }
+        p1 = coordinates.get(lowerIndex);
+        p2 = coordinates.get(middleIndex);
+        p3 = coordinates.get(upperIndex);
+        total += (rad(p3.longitude()) - rad(p1.longitude())) * Math.sin(rad(p2.latitude()));
+      }
+      total = total * EARTH_RADIUS * EARTH_RADIUS / 2;
+    }
+    return total;
+  }
+
+  private static double rad(double num) {
+    return num * Math.PI / 180;
+  }
 }

services-turf/src/test/java/com/mapbox/turf/TurfMeasurementTest.java

@@ -44,6 +44,14 @@ public class TurfMeasurementTest extends TestUtils {
   private static final String TURF_ENVELOPE_FEATURE_COLLECTION = "turf-envelope/feature-collection.geojson";
   private static final String LINE_DISTANCE_MULTILINESTRING
     = "turf-line-distance/multilinestring.geojson";
+  private static final String TURF_AREA_POLYGON_GEOJSON = "turf-area/polygon.geojson";
+  private static final String TURF_AREA_POLYGON_RESULT = "turf-area/polygon.json";
+  private static final String TURF_AREA_MULTIPOLYGON_GEOJSON = "turf-area/multi-polygon.geojson";
+  private static final String TURF_AREA_MULTIPOLYGON_RESULT = "turf-area/multi-polygon.json";
+  private static final String TURF_AREA_GEOM_POLYGON_GEOJSON = "turf-area/geometry-polygon.geojson";
+  private static final String TURF_AREA_GEOM_POLYGON_RESULT = "turf-area/geometry-polygon.json";
+  private static final String TURF_AREA_FEATURECOLLECTION_POLYGON_GEOJSON = "turf-area/featurecollection-polygon.geojson";
+  private static final String TURF_AREA_FEATURECOLLECTION_POLYGON_RESULT = "turf-area/featurecollection-polygon.json";
 
   @Rule
   public ExpectedException thrown = ExpectedException.none();
@@ -474,4 +482,30 @@ public void square(){
     assertEquals(BoundingBox.fromCoordinates(-2.5, 0, 7.5, 10), sq1);
     assertEquals(BoundingBox.fromCoordinates(0, -2.5, 10, 7.5), sq2);
   }
+
+  @Test
+  public void areaPolygon() {
+    double expected = Double.valueOf(loadJsonFixture(TURF_AREA_POLYGON_RESULT));
+    assertEquals(expected, TurfMeasurement.area(Feature.fromJson(loadJsonFixture(TURF_AREA_POLYGON_GEOJSON))), 1);
+  }
+
+  @Test
+  public void areaMultiPolygon() {
+    double expected = Double.valueOf(loadJsonFixture(TURF_AREA_MULTIPOLYGON_RESULT));
+    assertEquals(expected, TurfMeasurement.area(Feature.fromJson(loadJsonFixture(TURF_AREA_MULTIPOLYGON_GEOJSON))), 1);
+  }
+
+  @Test
+  public void areaGeometry() {
+    double expected = Double.valueOf(loadJsonFixture(TURF_AREA_GEOM_POLYGON_RESULT));
+    assertEquals(expected, TurfMeasurement.area(Polygon.fromJson(loadJsonFixture(TURF_AREA_GEOM_POLYGON_GEOJSON))), 1);
+  }
+
+  @Test
+  public void areaFeatureCollection() {
+    double expected = Double.valueOf(loadJsonFixture(TURF_AREA_FEATURECOLLECTION_POLYGON_RESULT));
+    assertEquals(expected, TurfMeasurement.area(FeatureCollection.fromJson(loadJsonFixture(TURF_AREA_FEATURECOLLECTION_POLYGON_GEOJSON))), 1);
+  }
+
+
 }

services-turf/src/test/resources/turf-area/featurecollection-polygon.geojson

@@ -0,0 +1,75 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [
+              -2.109375,
+              47.040182144806664
+            ],
+            [
+              4.5703125,
+              44.59046718130883
+            ],
+            [
+              7.03125,
+              49.15296965617042
+            ],
+            [
+              -3.515625,
+              49.83798245308484
+            ],
+            [
+              -2.109375,
+              47.040182144806664
+            ]
+          ]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [
+              9.64599609375,
+              47.70976154266637
+            ],
+            [
+              9.4482421875,
+              47.73932336136857
+            ],
+            [
+              8.8330078125,
+              47.47266286861342
+            ],
+            [
+              10.21728515625,
+              46.604167162931844
+            ],
+            [
+              11.755371093749998,
+              46.81509864599243
+            ],
+            [
+              11.865234375,
+              47.90161354142077
+            ],
+            [
+              9.64599609375,
+              47.70976154266637
+            ]
+          ]
+        ]
+      }
+    }
+  ]
+}

services-turf/src/test/resources/turf-area/featurecollection-polygon.json

@@ -0,0 +1 @@
+294852371360

services-turf/src/test/resources/turf-area/geometry-polygon.geojson

@@ -0,0 +1,10 @@
+{
+	"type": "Polygon",
+	"coordinates": [[
+		[-2.275543, 53.464547 ],
+		[-2.275543, 53.489271 ],
+		[-2.215118, 53.489271 ],
+		[-2.215118, 53.464547 ],
+		[-2.275543, 53.464547 ]
+	]]
+}

services-turf/src/test/resources/turf-area/geometry-polygon.json

@@ -0,0 +1 @@
+11017976

services-turf/src/test/resources/turf-area/multi-polygon.geojson

@@ -0,0 +1,60 @@
+{
+  "type": "Feature",
+  "properties": {
+    "stroke": "#F00",
+    "stroke-width": 6
+  },
+  "geometry": {
+    "type": "MultiPolygon",
+    "coordinates": [
+      [
+        [
+          [
+            102,
+            2
+          ],
+          [
+            103,
+            2
+          ],
+          [
+            103,
+            3
+          ],
+          [
+            102,
+            3
+          ],
+          [
+            102,
+            2
+          ]
+        ]
+      ],
+      [
+        [
+          [
+            100,
+            0
+          ],
+          [
+            101,
+            0
+          ],
+          [
+            101,
+            1
+          ],
+          [
+            100,
+            1
+          ],
+          [
+            100,
+            0
+          ]
+        ]
+      ]
+    ]
+  }
+}

services-turf/src/test/resources/turf-area/multi-polygon.json

@@ -0,0 +1 @@
+24771477332

services-turf/src/test/resources/turf-area/polygon.geojson

@@ -0,0 +1,19 @@
+{
+  "type": "Feature",
+  "properties": {},
+  "geometry": {
+    "type": "Polygon",
+    "coordinates": [
+      [
+        [125, -15],
+        [113, -22],
+        [117, -37],
+        [130, -33],
+        [148, -39],
+        [154, -27],
+        [144, -15],
+        [125, -15]
+      ]
+    ]
+  }
+}

services-turf/src/test/resources/turf-area/polygon.json

@@ -0,0 +1 @@
+7766240997209