source: osm/applications/viewer/jmapviewer/src/org/openstreetmap/gui/jmapviewer/OsmMercator.java@ 11376

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);
        }

}