[turf] Add polygonToLine method. (#1075)

* [turf] Add polygonToLine method.

* [turf] Fix the unit test by parsing json to Feature object and convert to json string again.

* [turf] Change since 4.9.0 to 4.10.0.

* [turf] Update change log and docs/turf-port.md

* [turf] Fix unit test.

Author: pengdev

CHANGELOG.md

@@ -5,6 +5,7 @@ Mapbox welcomes participation and contributions from everyone.
 ### master
 
 - 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)
 
 ### v4.9.0-alpha.1 - September 4, 2019
 

docs/turf-port.md

@@ -62,7 +62,7 @@ Below's an on going list of the Turf functions which currently exist inside the
 - [ ] turf-flatten
 - [ ] turf-line-to-polygon
 - [ ] turf-polygonize
-- [ ] turf-polygon-to-line
+- [x] turf-polygon-to-line
 
 ## Misc
 - [ ] turf-kinks

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

@@ -4,10 +4,17 @@
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 
+import com.google.gson.JsonObject;
 import com.mapbox.geojson.Feature;
 import com.mapbox.geojson.FeatureCollection;
+import com.mapbox.geojson.Geometry;
+import com.mapbox.geojson.LineString;
+import com.mapbox.geojson.MultiLineString;
+import com.mapbox.geojson.MultiPolygon;
 import com.mapbox.geojson.Point;
+import com.mapbox.geojson.Polygon;
 import com.mapbox.turf.TurfConstants.TurfUnitCriteria;
+import com.sun.istack.internal.NotNull;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -201,4 +208,142 @@ public static FeatureCollection explode(@NonNull Feature feature) {
     }
     return FeatureCollection.fromFeatures(finalFeatureList);
   }
+
+  /**
+   * Takes a {@link Feature} that contains {@link Polygon} and
+   * covert it to a {@link Feature} that contains {@link LineString} or {@link MultiLineString}.
+   *
+   * @param feature a {@link Feature} object that contains {@link Polygon}
+   * @return  a {@link Feature} object that contains {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static Feature polygonToLine(@NotNull Feature feature) {
+    return polygonToLine(feature, null);
+  }
+
+  /**
+   * Takes a {@link Feature} that contains {@link Polygon} and a properties {@link JsonObject} and
+   * covert it to a {@link Feature} that contains {@link LineString} or {@link MultiLineString}.
+   *
+   * @param feature a {@link Feature} object that contains {@link Polygon}
+   * @param properties a {@link JsonObject} that represents a feature's properties
+   * @return  a {@link Feature} object that contains {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static Feature polygonToLine(@NotNull Feature feature, @Nullable JsonObject properties) {
+    Geometry geometry = feature.geometry();
+    if (geometry instanceof Polygon) {
+      return polygonToLine((Polygon) geometry,properties != null ? properties :
+              feature.type().equals("Feature") ? feature.properties() : new JsonObject());
+    }
+    throw new TurfException("Feature's geometry must be Polygon");
+  }
+
+  /**
+   * Takes a {@link Polygon} and
+   * covert it to a {@link Feature} that contains {@link LineString} or {@link MultiLineString}.
+   *
+   * @param polygon a {@link Polygon} object
+   * @return  a {@link Feature} object that contains {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static Feature polygonToLine(@NotNull Polygon polygon) {
+    return polygonToLine(polygon, null);
+  }
+
+  /**
+   * Takes a {@link MultiPolygon} and
+   * covert it to a {@link FeatureCollection} that contains list
+   * of {@link Feature} of {@link LineString} or {@link MultiLineString}.
+   *
+   * @param multiPolygon a {@link MultiPolygon} object
+   * @return  a {@link FeatureCollection} object that contains
+   *   list of {@link Feature} of {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static FeatureCollection polygonToLine(@NotNull MultiPolygon multiPolygon) {
+    return polygonToLine(multiPolygon, null);
+  }
+
+  /**
+   * Takes a {@link Polygon} and a properties {@link JsonObject} and
+   * covert it to a {@link Feature} that contains {@link LineString} or {@link MultiLineString}.
+   *
+   * @param polygon a {@link Polygon} object
+   * @param properties a {@link JsonObject} that represents a feature's properties
+   * @return  a {@link Feature} object that contains {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static Feature polygonToLine(@NotNull Polygon polygon, @Nullable JsonObject properties) {
+    return coordsToLine(polygon.coordinates(), properties);
+  }
+
+  /**
+   * Takes a {@link MultiPolygon} and a properties {@link JsonObject} and
+   * covert it to a {@link FeatureCollection} that contains list
+   * of {@link Feature} of {@link LineString} or {@link MultiLineString}.
+   *
+   * @param multiPolygon a {@link MultiPolygon} object
+   * @param properties a {@link JsonObject} that represents a feature's properties
+   * @return  a {@link FeatureCollection} object that contains
+   *   list of {@link Feature} of {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static FeatureCollection polygonToLine(@NotNull MultiPolygon multiPolygon,
+                                                @Nullable JsonObject properties) {
+    List<List<List<Point>>> coordinates = multiPolygon.coordinates();
+    List<Feature> finalFeatureList = new ArrayList<>();
+    for (List<List<Point>> polygonCoordinates : coordinates) {
+      finalFeatureList.add(coordsToLine(polygonCoordinates, properties));
+    }
+    return FeatureCollection.fromFeatures(finalFeatureList);
+  }
+
+  /**
+   * Takes a {@link Feature} that contains {@link MultiPolygon} and
+   * covert it to a {@link FeatureCollection} that contains list of {@link Feature}
+   * of {@link LineString} or {@link MultiLineString}.
+   *
+   * @param feature a {@link Feature} object that contains {@link Polygon}
+   * @return  a {@link FeatureCollection} object that contains list of {@link Feature}
+   *   of {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static FeatureCollection multiPolygonToLine(@NotNull Feature feature) {
+    return multiPolygonToLine(feature, null);
+  }
+
+  /**
+   * Takes a {@link Feature} that contains {@link MultiPolygon} and a
+   * properties {@link JsonObject} and
+   * covert it to a {@link FeatureCollection} that contains
+   * list of {@link Feature} of {@link LineString} or {@link MultiLineString}.
+   *
+   * @param feature a {@link Feature} object that contains {@link MultiPolygon}
+   * @param properties a {@link JsonObject} that represents a feature's properties
+   * @return  a {@link FeatureCollection} object that contains
+   *   list of {@link Feature} of {@link LineString} or {@link MultiLineString}
+   * @since 4.10.0
+   */
+  public static FeatureCollection multiPolygonToLine(@NotNull Feature feature,
+                                                     @Nullable JsonObject properties) {
+    Geometry geometry = feature.geometry();
+    if (geometry instanceof MultiPolygon) {
+      return polygonToLine((MultiPolygon) geometry, properties != null ? properties :
+              feature.type().equals("Feature") ? feature.properties() : new JsonObject());
+    }
+    throw new TurfException("Feature's geometry must be MultiPolygon");
+  }
+
+  @Nullable
+  private static Feature coordsToLine(@NotNull List<List<Point>> coordinates,
+                                      @Nullable JsonObject properties) {
+    if (coordinates.size() > 1) {
+      return Feature.fromGeometry(MultiLineString.fromLngLats(coordinates), properties);
+    } else if (coordinates.size() == 1) {
+      LineString lineString = LineString.fromLngLats(coordinates.get(0));
+      return Feature.fromGeometry(lineString, properties);
+    }
+    return null;
+  }
 }

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

@@ -6,11 +6,15 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
+import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;
+import java.net.URL;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Scanner;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
@@ -27,7 +31,7 @@ public void compareJson(String expectedJson, String actualJson) {
     assertThat(parser.parse(actualJson), Matchers.equalTo(parser.parse(expectedJson)));
   }
 
-  protected String loadJsonFixture(String filename) throws IOException {
+  protected String loadJsonFixture(String filename) {
     ClassLoader classLoader = getClass().getClassLoader();
     InputStream inputStream = classLoader.getResourceAsStream(filename);
     Scanner scanner = new Scanner(inputStream, UTF_8.name()).useDelimiter("\\A");
@@ -58,4 +62,15 @@ public static void expectNearNumber(double expected, double actual, double epsil
     assertTrue(String.format("Expected %f to be near %f", actual, expected),
       Math.abs(expected - actual) <= epsilon);
   }
+
+  protected List<String> getResourceFolderFileNames (String folder) {
+    ClassLoader loader = getClass().getClassLoader();
+    URL url = loader.getResource(folder);
+    String path = url.getPath();
+    List<String> names = new ArrayList<>();
+    for (File file : new File(path).listFiles()) {
+      names.add(file.getName());
+    }
+    return names;
+  }
 }

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

@@ -27,11 +27,23 @@ public class TurfConversionTest extends TestUtils {
   private static final String TURF_EXPLODE_MULTIPOLYGON = "turf-explode/multipolygon.geojson";
   private static final String TURF_EXPLODE_GEOMETRY_COLLECTION = "turf-explode/geometrycollection.geojson";
 
+  private static final String TURF_POLYGON_TO_LINE_PATH_IN = "turf-polygon-to-line/in/";
+  private static final String TURF_POLYGON_TO_LINE_PATH_OUT = "turf-polygon-to-line/expected/";
+
+  private static final String TURF_POLYGON_TO_LINE_FILENAME_POLYGON= "polygon.geojson";
+  private static final String TURF_POLYGON_TO_LINE_FILENAME_GEOMETRY_POLYGON= "geometry-polygon.geojson";
+  private static final String TURF_POLYGON_TO_LINE_FILENAME_POLYGON_WITH_HOLE = "polygon-with-hole.geojson";
+
+  private static final String TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON = "multi-polygon.geojson";
+  private static final String TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON_OUTER_DOUGHNUT = "multi-polygon-outer-doughnut.geojson";
+  private static final String TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON_WITH_HOLES = "multi-polygon-with-holes.geojson";
+
+
   @Rule
   public ExpectedException thrown = ExpectedException.none();
 
   @Test
-  public void radiansToDistance() throws Exception {
+  public void radiansToDistance() {
     assertEquals(
       1, TurfConversion.radiansToLength(1, TurfConstants.UNIT_RADIANS), DELTA);
     assertEquals(
@@ -41,7 +53,7 @@ public void radiansToDistance() throws Exception {
   }
 
   @Test
-  public void distanceToRadians() throws Exception {
+  public void distanceToRadians() {
     assertEquals(
       1, TurfConversion.lengthToRadians(1, TurfConstants.UNIT_RADIANS), DELTA);
     assertEquals(
@@ -51,7 +63,7 @@ public void distanceToRadians() throws Exception {
   }
 
   @Test
-  public void distanceToDegrees() throws Exception {
+  public void distanceToDegrees() {
     assertEquals(
       57.29577951308232, TurfConversion.lengthToDegrees(1, TurfConstants.UNIT_RADIANS), DELTA);
     assertEquals(
@@ -79,25 +91,25 @@ public void convertDistance() throws TurfException {
   }
 
   @Test
-  public void explodePointSingleFeature() throws IOException, NullPointerException {
+  public void explodePointSingleFeature() throws NullPointerException {
     Point point = Point.fromLngLat(102, 0.5);
     assertEquals(1, TurfConversion.explode(Feature.fromGeometry(point)).features().size());
   }
 
   @Test
-  public void explodeMultiPointSingleFeature() throws IOException, NullPointerException {
+  public void explodeMultiPointSingleFeature() throws NullPointerException {
     MultiPoint multiPoint = MultiPoint.fromJson(loadJsonFixture(TURF_EXPLODE_MULTI_POINT));
     assertEquals(4, TurfConversion.explode(Feature.fromGeometry(multiPoint)).features().size());
   }
 
   @Test
-  public void explodeLineStringSingleFeature() throws IOException, NullPointerException {
+  public void explodeLineStringSingleFeature() throws NullPointerException {
     LineString lineString = LineString.fromJson(loadJsonFixture(TURF_EXPLODE_LINESTRING));
     assertEquals(4, TurfConversion.explode(Feature.fromGeometry(lineString)).features().size());
   }
 
   @Test
-  public void explodePolygonSingleFeature() throws IOException, NullPointerException {
+  public void explodePolygonSingleFeature() throws NullPointerException {
     Polygon polygon = Polygon.fromLngLats(Arrays.asList(
       Arrays.asList(
         Point.fromLngLat(0, 101),
@@ -108,29 +120,71 @@ public void explodePolygonSingleFeature() throws IOException, NullPointerExcepti
   }
 
   @Test
-  public void explodeMultiLineStringSingleFeature() throws IOException, NullPointerException {
+  public void explodeMultiLineStringSingleFeature() throws NullPointerException {
     MultiLineString multiLineString = MultiLineString.fromJson(loadJsonFixture(TURF_EXPLODE_MULTILINESTRING));
     assertEquals(4, TurfConversion.explode(Feature.fromGeometry(multiLineString)).features().size());
   }
 
   @Test
-  public void explodeMultiPolygonSingleFeature() throws IOException, NullPointerException {
+  public void explodeMultiPolygonSingleFeature() throws NullPointerException {
     MultiPolygon multiPolygon = MultiPolygon.fromJson(loadJsonFixture(TURF_EXPLODE_MULTIPOLYGON));
     assertEquals(12, TurfConversion.explode(Feature.fromGeometry(multiPolygon)).features().size());
   }
 
   @Test
-  public void explodeGeometryCollectionSingleFeature() throws IOException, NullPointerException {
+  public void explodeGeometryCollectionSingleFeature() throws NullPointerException {
     GeometryCollection geometryCollection = GeometryCollection.fromJson(loadJsonFixture(TURF_EXPLODE_GEOMETRY_COLLECTION));
     assertEquals(3, TurfConversion.explode(Feature.fromGeometry(geometryCollection)).features().size());
   }
 
   @Test
-  public void explodeFeatureCollection() throws IOException, NullPointerException {
+  public void explodeFeatureCollection() throws NullPointerException {
     FeatureCollection featureCollection = FeatureCollection.fromFeatures(new Feature[] {
       Feature.fromGeometry(MultiLineString.fromJson(loadJsonFixture(TURF_EXPLODE_MULTILINESTRING))),
       Feature.fromGeometry(MultiPolygon.fromJson(loadJsonFixture(TURF_EXPLODE_MULTIPOLYGON)))
     });
     assertEquals(16, TurfConversion.explode(featureCollection).features().size());
   }
+
+  @Test
+  public void polygonToLine_GeometryPolygon() throws NullPointerException {
+    Polygon polygon = Polygon.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_IN + TURF_POLYGON_TO_LINE_FILENAME_GEOMETRY_POLYGON));
+    Feature expected = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_OUT + TURF_POLYGON_TO_LINE_FILENAME_GEOMETRY_POLYGON));
+    compareJson(expected.toJson(), TurfConversion.polygonToLine(polygon).toJson());
+  }
+
+  @Test
+  public void polygonToLine_Polygon() throws NullPointerException {
+    Feature polygon = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_IN + TURF_POLYGON_TO_LINE_FILENAME_POLYGON));
+    Feature expected = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_OUT + TURF_POLYGON_TO_LINE_FILENAME_POLYGON));
+    compareJson(expected.toJson(), TurfConversion.polygonToLine(polygon).toJson());
+  }
+
+  @Test
+  public void polygonToLine_PolygonWithHole() throws NullPointerException {
+    Feature polygon = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_IN + TURF_POLYGON_TO_LINE_FILENAME_POLYGON_WITH_HOLE));
+    Feature expected = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_OUT + TURF_POLYGON_TO_LINE_FILENAME_POLYGON_WITH_HOLE));
+    compareJson(expected.toJson(), TurfConversion.polygonToLine(polygon).toJson());
+  }
+
+  @Test
+  public void polygonToLine_MultiPolygon() throws NullPointerException {
+    Feature multiPolygon = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_IN + TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON));
+    FeatureCollection expected = FeatureCollection.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_OUT + TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON));
+    compareJson(expected.toJson(), TurfConversion.multiPolygonToLine(multiPolygon).toJson());
+  }
+
+  @Test
+  public void polygonToLine_MultiPolygonWithHoles() throws NullPointerException {
+    Feature multiPolygon = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_IN + TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON_WITH_HOLES));
+    FeatureCollection expected = FeatureCollection.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_OUT + TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON_WITH_HOLES));
+    compareJson(expected.toJson(), TurfConversion.multiPolygonToLine(multiPolygon).toJson());
+  }
+
+  @Test
+  public void polygonToLine_MultiPolygonWithOuterDoughnut() throws NullPointerException {
+    Feature multiPolygon = Feature.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_IN + TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON_OUTER_DOUGHNUT));
+    FeatureCollection expected = FeatureCollection.fromJson(loadJsonFixture(TURF_POLYGON_TO_LINE_PATH_OUT + TURF_POLYGON_TO_LINE_FILENAME_MULTIPOLYGON_OUTER_DOUGHNUT));
+    compareJson(expected.toJson(), TurfConversion.multiPolygonToLine(multiPolygon).toJson());
+  }
 }

services-turf/src/test/resources/turf-polygon-to-line/expected/geometry-polygon.geojson

@@ -0,0 +1,29 @@
+{
+	"type": "Feature",
+	"properties": {},
+	"geometry": {
+		"type": "LineString",
+		"coordinates": [
+			[
+				-2.275543,
+				53.464547
+			],
+			[
+				-2.275543,
+				53.489271
+			],
+			[
+				-2.215118,
+				53.489271
+			],
+			[
+				-2.215118,
+				53.464547
+			],
+			[
+				-2.275543,
+				53.464547
+			]
+		]
+	}
+}