added convert distance method to TurfHelper

mapbox/libjava-services/src/main/java/com/mapbox/services/api/utils/turf/TurfConstants.java

@@ -16,6 +16,8 @@ public class TurfConstants {
   public static final String UNIT_INCHES = "inches";
   public static final String UNIT_YARDS = "yards";
   public static final String UNIT_METERS = "meters";
+  public static final String UNIT_CENTIMETERS = "centimeters";
+  public static final String UNIT_FEET = "feet";
 
   public static final String UNIT_DEFAULT = UNIT_KILOMETERS;
 

mapbox/libjava-services/src/main/java/com/mapbox/services/api/utils/turf/TurfHelpers.java

@@ -23,9 +23,12 @@ public class TurfHelpers {
     factors.put(TurfConstants.UNIT_INCHES, 250905600d);
     factors.put(TurfConstants.UNIT_YARDS, 6969600d);
     factors.put(TurfConstants.UNIT_METERS, 6373000d);
+    factors.put(TurfConstants.UNIT_CENTIMETERS, 6.373e+8d);
     factors.put(TurfConstants.UNIT_KILOMETERS, 6373d);
+    factors.put(TurfConstants.UNIT_FEET, 20908792.65d);
 
     // Also supported
+    factors.put("centimetres", 6.373e+8d);
     factors.put("metres", 6373000d);
     factors.put("kilometres", 6373d);
   }
@@ -88,4 +91,41 @@ public static double distanceToRadians(double distance, String units) throws Tur
     }
     return distance / factor;
   }
+
+  /**
+   * Converts a distance to the requested unit.
+   * Valid units: miles, nauticalmiles, inches, yards, meters, metres, kilometers, centimeters, feet
+   *
+   * @param distance     the distance to be converted
+   * @param originalUnit of the distance
+   * @return the converted distance
+   * @since 2.2.0
+   */
+  public static double convertDistance(double distance, String originalUnit) {
+    return convertDistance(distance, originalUnit, TurfConstants.UNIT_DEFAULT);
+  }
+
+  /**
+   * Converts a distance to the requested unit.
+   * Valid units: miles, nauticalmiles, inches, yards, meters, metres, kilometers, centimeters, feet
+   *
+   * @param distance     the distance to be converted
+   * @param originalUnit of the distance
+   * @param finalUnit    returned unit, {@link TurfConstants#UNIT_DEFAULT} if not specified.
+   * @return the converted distance
+   * @since 2.2.0
+   */
+  public static double convertDistance(double distance, String originalUnit, String finalUnit) {
+    Double factor = factors.get(originalUnit);
+    if (factor == null) {
+      throw new TurfException("Invalid unit.");
+    } else if (!(distance >= 0)) {
+      throw new TurfException("Distance must be a positive number.");
+    }
+    if (finalUnit == null) {
+      finalUnit = TurfConstants.UNIT_DEFAULT;
+    }
+
+    return radiansToDistance(distanceToRadians(distance, originalUnit), finalUnit);
+  }
 }

mapbox/libjava-services/src/test/java/com/mapbox/services/api/turf/TurfHelpersTest.java

@@ -0,0 +1,47 @@
+package com.mapbox.services.api.turf;
+
+import com.mapbox.services.api.BaseTest;
+import com.mapbox.services.api.utils.turf.TurfConstants;
+import com.mapbox.services.api.utils.turf.TurfException;
+import com.mapbox.services.api.utils.turf.TurfHelpers;
+
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import static org.hamcrest.Matchers.startsWith;
+
+public class TurfHelpersTest extends BaseTest {
+
+  @Rule
+  public ExpectedException thrown = ExpectedException.none();
+
+  @Test
+  public void convertDistance_throwNegativeDistanceException() throws TurfException {
+    thrown.expect(TurfException.class);
+    thrown.expectMessage(startsWith("Distance must be a"));
+    TurfHelpers.convertDistance(-1, TurfConstants.UNIT_MILES);
+  }
+
+  @Test
+  public void convertDistance_throwInvalidUnitException() throws TurfException {
+    thrown.expect(TurfException.class);
+    thrown.expectMessage(startsWith("Invalid unit."));
+    TurfHelpers.convertDistance(1, "foo");
+  }
+
+  @Test
+  public void convertDistance() throws TurfException {
+    Assert.assertEquals(1,
+      TurfHelpers.convertDistance(1000, TurfConstants.UNIT_METERS), DELTA);
+    Assert.assertEquals(0.6213714106386318,
+      TurfHelpers.convertDistance(1, TurfConstants.UNIT_KILOMETERS, TurfConstants.UNIT_MILES), DELTA);
+    Assert.assertEquals(1.6093434343434343,
+      TurfHelpers.convertDistance(1, TurfConstants.UNIT_MILES, TurfConstants.UNIT_KILOMETERS), DELTA);
+    Assert.assertEquals(1.851999843075488,
+      TurfHelpers.convertDistance(1, TurfConstants.UNIT_NAUTICAL_MILES), DELTA);
+    Assert.assertEquals(100,
+      TurfHelpers.convertDistance(1, TurfConstants.UNIT_METERS, TurfConstants.UNIT_CENTIMETERS), DELTA);
+  }
+}