Merge pull request #899 from conveyal/merge-pixel-functions

Merge WGS84 / web Mercator conversion functions

src/main/java/com/conveyal/r5/analyst/Grid.java

@@ -8,7 +8,6 @@
 import com.csvreader.CsvReader;
 import com.google.common.io.LittleEndianDataInputStream;
 import com.google.common.io.LittleEndianDataOutputStream;
-import org.apache.commons.math3.util.FastMath;
 import org.geotools.coverage.grid.GridCoverage2D;
 import org.geotools.coverage.grid.GridCoverageFactory;
 import org.geotools.coverage.grid.io.AbstractGridFormat;
@@ -64,15 +63,17 @@
 
 import static com.conveyal.gtfs.util.Util.human;
 import static com.conveyal.r5.common.GeometryUtils.checkWgsEnvelopeSize;
-import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkState;
 import static java.lang.Double.parseDouble;
-import static org.apache.commons.math3.util.FastMath.atan;
-import static org.apache.commons.math3.util.FastMath.cos;
-import static org.apache.commons.math3.util.FastMath.log;
-import static org.apache.commons.math3.util.FastMath.sinh;
-import static org.apache.commons.math3.util.FastMath.tan;
-import static org.apache.commons.math3.util.FastMath.toRadians;
+import static java.lang.Math.PI;
+import static java.lang.Math.atan;
+import static java.lang.Math.cos;
+import static java.lang.Math.log;
+import static java.lang.Math.pow;
+import static java.lang.Math.sinh;
+import static java.lang.Math.tan;
+import static java.lang.Math.toDegrees;
+import static java.lang.Math.toRadians;
 
 /**
  * Class that represents a grid of opportunity counts in the spherical Mercator "projection" at a given zoom level.
@@ -482,7 +483,7 @@ public static int lonToPixel (double lon, int zoom) {
      * Naming should somehow be revised to clarify that it doesn't return the center of the pixel.
      */
     public static double pixelToLon (double xPixel, int zoom) {
-        return xPixel / (Math.pow(2, zoom) * 256) * 360 - 180;
+        return xPixel / (pow(2, zoom) * 256) * 360 - 180;
     }
 
     /**
@@ -505,20 +506,24 @@ public static int latToPixel (double lat, int zoom) {
     }
 
     /**
-     * Return the latitude of the center of all pixels at the given zoom level and absolute (world) y pixel number
-     * measured southward from the north edge of the world.
+     * Given an integer web Mercator pixel number, return the latitude in degrees of the north edge of that pixel at the
+     * given zoom level relative to the top (north) edge of the world (not relative to this grid or to any particular
+     * tile). Given a non-integer web Mercator pixel number, return WGS84 locations within that pixel.
+     *
+     * TODO Profile this some time because we had versions using both FastMath and built-in Math functions.
+     * The difference should be less significant these days. Java now has a StrictMath and the normal Math is optimized.
      */
-    public static double pixelToCenterLat (int yPixel, int zoom) {
-        return pixelToLat(yPixel + 0.5, zoom);
+    public static double pixelToLat (double yPixel, int zoom) {
+        final double tile = yPixel / 256d;
+        return toDegrees(atan(sinh(PI - tile * PI * 2 / pow(2, zoom))));
     }
 
     /**
-     * Return the latitude of the north edge of any pixel at the given zoom level and y coordinate relative to the top
-     * edge of the world (assuming an integer pixel). Noninteger pixels will return locations within the pixel.
-     * We're using FastMath here, because the built-in math functions were taking a large amount of time in profiling.
+     * Return the latitude of the center of all pixels at the given zoom level and absolute (world) y pixel number
+     * measured southward from the north edge of the world.
      */
-    public static double pixelToLat (double yPixel, int zoom) {
-        return FastMath.toDegrees(atan(sinh(Math.PI - (yPixel / 256d) / Math.pow(2, zoom) * 2 * Math.PI)));
+    public static double pixelToCenterLat (int yPixel, int zoom) {
+        return pixelToLat(yPixel + 0.5, zoom);
     }
 
     /**