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[turf] Add turf area measurement method. (#1079)
* [turf] Add turf area measurement method and test. * [turf] Add javadoc. * [turf] Add more test cases. * [turf] Update change log. * [turf] Change turf area since to 4.10.0
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‎CHANGELOG.md‎

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

‎docs/turf-port.md‎

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

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

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

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

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

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

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

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

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294852371360

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

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{
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"type": "Polygon",
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"coordinates": [[
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[-2.275543, 53.464547 ],
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[-2.275543, 53.489271 ],
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[-2.215118, 53.489271 ],
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[-2.215118, 53.464547 ],
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[-2.275543, 53.464547 ]
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]]
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}

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

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11017976

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

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

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

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24771477332

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