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Combine WGS84 to web Mercator functions
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WebMercatorGridPointSet methods now call static Grid functions with zoom.
All functions are now using standard Java Math (not FastMath).
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@abyrd
abyrd committed Oct 16, 2023
1 parent 1eaa461 commit 8b1fdce
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Showing 2 changed files with 24 additions and 45 deletions.
32 changes: 16 additions & 16 deletions src/main/java/com/conveyal/r5/analyst/Grid.java
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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;
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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 java.lang.Math.*;

/**
* Class that represents a grid of opportunity counts in the spherical Mercator "projection" at a given zoom level.
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/** Like lonToPixel but returns fractional values for positions within a pixel instead of integer pixel numbers. */
public static double lonToFractionalPixel (double lon, int zoom) {
// Factor of 256 yields a pixel value rather than the tile number.
return (lon + 180) / 360 * Math.pow(2, zoom) * 256;
}

Expand All @@ -474,12 +469,13 @@ public static int lonToPixel (double lon, int zoom) {
}

/**
* Return the longitude of the west edge of any pixel at the given zoom level and x pixel number measured from the
* west edge of the world (assuming an integer x pixel number). Noninteger x pixel coordinates will return
* WGS84 locations within that pixel.
* Given an integer web Mercator pixel number, return the longitude in degrees of the west edge of that pixel at
* the given zoom level measured from the west 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.
* 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;
}

/**
Expand All @@ -492,7 +488,7 @@ public static double pixelToCenterLon (int xPixel, int zoom) {

/** Like latToPixel but returns fractional values for positions within a pixel instead of integer pixel numbers. */
public static double latToFractionalPixel (double lat, int zoom) {
double latRad = FastMath.toRadians(lat);
final double latRad = toRadians(lat);
return (1 - log(tan(latRad) + 1 / cos(latRad)) / Math.PI) * Math.pow(2, zoom - 1) * 256;
}

Expand All @@ -502,12 +498,16 @@ public static int latToPixel (double lat, int 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.
* 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 pixelToLat (double yPixel, int zoom) {
return FastMath.toDegrees(atan(sinh(Math.PI - (yPixel / 256d) / Math.pow(2, zoom) * 2 * Math.PI)));
final double tile = yPixel / 256d;
return toDegrees(atan(sinh(PI - tile * PI * 2 / pow(2, zoom))));
}

/**
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37 changes: 8 additions & 29 deletions src/main/java/com/conveyal/r5/analyst/WebMercatorGridPointSet.java
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Expand Up @@ -150,54 +150,33 @@ public TIntList getPointsInEnvelope (Envelope envelopeFixedDegrees) {
}

// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Mathematics
// FIXME Grid.java has seemingly identical definitions of these same mercator-to-wgs methods.
// These methods should just be wrappers that pass in this WebMercatorGridPointSet's zoom level.
// Grid also has methods that distinguish between pixel corner and center. Those corner methods should be renamed.
// WebMercatorGridPointSet, Grid, and WebMercatorExtents are in the same package and should share methods.

/**
* Return the x pixel number containing the given longitude at this grid's zoom level, relative to the left edge
* of the world (not relative to this grid or to any particular tile).
* TODO This method could be reusable and static if zoom level was a parameter. And moved to WebMercatorExtents.
* See com.conveyal.r5.analyst.Grid#lonToPixel(double, int)
*/
public int lonToPixel (double lon) {
// factor of 256 is to get a pixel value not a tile number
return (int) ((lon + 180) / 360 * Math.pow(2, zoom) * 256);
return Grid.lonToPixel(lon, zoom);
}

/**
* Return the y pixel number containing the given latitude at this grid's zoom level, relative to the top edge of
* the world (not relative to this grid or to any particular tile).
* TODO This method could be reusable and static if zoom level was a parameter. And moved to WebMercatorExtents.
* See com.conveyal.r5.analyst.Grid#latToPixel(double, int)
*/
public int latToPixel (double lat) {
double invCos = 1 / Math.cos(Math.toRadians(lat));
double tan = Math.tan(Math.toRadians(lat));
double ln = Math.log(tan + invCos);
return (int) ((1 - ln / Math.PI) * Math.pow(2, zoom - 1) * 256);
return Grid.latToPixel(lat, zoom);
}

/**
* Return the longitude in degrees of the west edge of any pixel at the specified x coordinate relative to the left
* edge of the world (not relative to this grid or to any particular tile), at this grid's zoom level.
* TODO This method could be reusable and static if zoom level was a parameter.
* It should probably also be renamed to clarify that it doesn't return the center of the pixel.
* Another equivalent method is found in Grid, and should probably be merged with this one and WebMercatorExtents.
* See com.conveyal.r5.analyst.Grid#pixelToLon(double, int)
*/
public double pixelToLon (double x) {
return x / (Math.pow(2, zoom) * 256) * 360 - 180;
return Grid.pixelToLon(x, zoom);
}

/**
* Return the latitude in degrees of the north edge of any pixel at the specified y coordinate relative to the top
* edge of the world (not relative to this grid or to any particular tile), at this grid's zoom level.
* TODO This method could be reusable and static if zoom level was a parameter.
* It should probably also be renamed to clarify that it doesn't return the center of the pixel.
* Another equivalent method is found in Grid, and should probably be merged with this one and WebMercatorExtents.
* See com.conveyal.r5.analyst.Grid#pixelToLat(double, int)
*/
public double pixelToLat (double y) {
double tile = y / 256d;
return Math.toDegrees(Math.atan(Math.sinh(Math.PI - tile * Math.PI * 2 / Math.pow(2, zoom))));
return Grid.pixelToLat(y, zoom);
}

@Override
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