source: osm/applications/viewer/jmapviewer/src/org/openstreetmap/gui/jmapviewer/OsmMercator.java@ 14053

package org.openstreetmap.gui.jmapviewer;

// License: GPL. Copyright 2007 by Tim Haussmann

/**
 * This class implements the Mercator Projection as it is used by Openstreetmap
 * (and google). It provides methods to translate coordinates from 'map space'
 * into latitude and longitude (on the WGS84 ellipsoid) and vice versa. Map
 * space is measured in pixels. The origin of the map space is the top left
 * corner. The map space origin (0,0) has latitude ~85 and longitude -180
 * 
 * @author Tim Haussmann
 * 
 */

public class OsmMercator {

    private static int TILE_SIZE = 256;
    public static final double MAX_LAT = 85.05112877980659;
    public static final double MIN_LAT = -85.05112877980659;

    public static double radius(int aZoomlevel) {
        return (TILE_SIZE * (1 << aZoomlevel)) / (2.0 * Math.PI);
    }

    /**
     * Returns the absolut number of pixels in y or x, defined as: 2^Zoomlevel *
     * TILE_WIDTH where TILE_WIDTH is the width of a tile in pixels
     * 
     * @param aZoomlevel
     * @return
     */
    public static int getMaxPixels(int aZoomlevel) {
        return TILE_SIZE * (1 << aZoomlevel);
    }

    public static int falseEasting(int aZoomlevel) {
        return getMaxPixels(aZoomlevel) / 2;
    }

    public static int falseNorthing(int aZoomlevel) {
        return (-1 * getMaxPixels(aZoomlevel) / 2);
    }

    /**
     * Transform longitude to pixelspace
     * 
     * @param aLongitude
     *            [-180..180]
     * @return [0..2^Zoomlevel*TILE_SIZE[
     */
    public static int LonToX(double aLongitude, int aZoomlevel) {
        double longitude = Math.toRadians(aLongitude);
        int x = (int) ((radius(aZoomlevel) * longitude) + falseEasting(aZoomlevel));
        x = Math.min(x, getMaxPixels(aZoomlevel) - 1);
        return x;
    }

    /**
     * Transforms latitude to pixelspace
     * 
     * @param aLat
     *            [-90...90]
     * @return [0..2^Zoomlevel*TILE_SIZE[
     */
    public static int LatToY(double aLat, int aZoomlevel) {
        if (aLat < MIN_LAT)
            aLat = MIN_LAT;
        else if (aLat > MAX_LAT)
            aLat = MAX_LAT;
        double latitude = Math.toRadians(aLat);
        int y = (int) (-1
                * (radius(aZoomlevel) / 2.0 * Math.log((1.0 + Math.sin(latitude)) / (1.0 - Math.sin(latitude)))) - falseNorthing(aZoomlevel));
        y = Math.min(y, getMaxPixels(aZoomlevel) - 1);
        return y;
    }

    /**
     * Transforms pixel coordinate X to longitude
     * 
     * @param aX
     *            [0..2^Zoomlevel*TILE_WIDTH[
     * @return ]-180..180[
     */
    public static double XToLon(int aX, int aZoomlevel) {
        aX -= falseEasting(aZoomlevel);
        double longRadians = aX / radius(aZoomlevel);
        double longDegrees = Math.toDegrees(longRadians);
        return longDegrees;
    }

    /**
     * Transforms pixel coordinate Y to latitude
     * 
     * @param aY
     *            [0..2^Zoomlevel*TILE_WIDTH[
     * @return [MIN_LAT..MAX_LAT] is about [-85..85]
     */
    public static double YToLat(int aY, int aZoomlevel) {
        aY += falseNorthing(aZoomlevel);
        double latitude = (Math.PI / 2) - (2 * Math.atan(Math.exp(-1.0 * aY / radius(aZoomlevel))));
        return -1 * Math.toDegrees(latitude);
    }

}