source: josm/trunk/src/org/openstreetmap/josm/data/coor/QuadTiling.java@ 10747

// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.data.coor;

import org.openstreetmap.josm.tools.Utils;

public final class QuadTiling {

    private QuadTiling() {
        // Hide default constructor for utils classes
    }

    public static final int NR_LEVELS = 24;
    public static final double WORLD_PARTS = 1 << NR_LEVELS;

    public static final int TILES_PER_LEVEL_SHIFT = 2; // Has to be 2. Other parts of QuadBuckets code rely on it
    public static final int TILES_PER_LEVEL = 1 << TILES_PER_LEVEL_SHIFT;
    public static final int X_PARTS = 360;
    public static final int X_BIAS = -180;

    public static final int Y_PARTS = 180;
    public static final int Y_BIAS = -90;

    public static LatLon tile2LatLon(long quad) {
        // The world is divided up into X_PARTS,Y_PARTS.
        // The question is how far we move for each bit being set.
        // In the case of the top level, we move half of the world.
        double xUnit = X_PARTS/2d;
        double yUnit = Y_PARTS/2d;
        long shift = (NR_LEVELS*2L)-2L;

        double x = 0;
        double y = 0;
        for (int i = 0; i < NR_LEVELS; i++) {
            long bits = (quad >> shift) & 0x3;
            // remember x is the MSB
            if ((bits & 0x2) != 0) {
                x += xUnit;
            }
            if ((bits & 0x1) != 0) {
                y += yUnit;
            }
            xUnit /= 2;
            yUnit /= 2;
            shift -= 2;
        }
        x += X_BIAS;
        y += Y_BIAS;
        return new LatLon(y, x);
    }

    static long xy2tile(long x, long y) {
        long tile = 0;
        int i;
        for (i = NR_LEVELS-1; i >= 0; i--) {
            long xbit = (x >> i) & 1;
            long ybit = (y >> i) & 1;
            tile <<= 2;
            // Note that x is the MSB
            tile |= (xbit << 1) | ybit;
        }
        return tile;
    }

    static long lon2x(double lon) {
        long ret = (long) ((lon + 180.0) * WORLD_PARTS / 360.0);
        if (Utils.equalsEpsilon(ret, WORLD_PARTS)) {
            ret--;
        }
        return ret;
    }

    static long lat2y(double lat) {
        long ret = (long) ((lat + 90.0) * WORLD_PARTS / 180.0);
        if (Utils.equalsEpsilon(ret, WORLD_PARTS)) {
            ret--;
        }
        return ret;
    }

    public static long quadTile(LatLon coor) {
        return xy2tile(lon2x(coor.lon()), lat2y(coor.lat()));
    }

    public static int index(int level, long quad) {
        long mask = 0x00000003;
        int totalShift = TILES_PER_LEVEL_SHIFT*(NR_LEVELS-level-1);
        return (int) (mask & (quad >> totalShift));
    }

    /**
     * Returns quad tiling index for given coordinates and level.
     *
     * @param coor coordinates
     * @param level level
     *
     * @return quad tiling index for given coordinates and level.
     * @since 2263
     */
    public static int index(LatLon coor, int level) {
        // The nodes that don't return coordinates will all get stuck in a single tile.
        // Hopefully there are not too many of them
        if (coor == null)
            return 0;

        return index(coor.lat(), coor.lon(), level);
    }

    /**
     * Returns quad tiling index for given coordinates and level.
     *
     * @param lat latitude
     * @param lon longitude
     * @param level level
     *
     * @return quad tiling index for given coordinates and level.
     * @since 6171
     */
    public static int index(final double lat, final double lon, final int level) {
        long x = lon2x(lon);
        long y = lat2y(lat);
        int shift = NR_LEVELS-level-1;
        return (int) ((x >> shift & 1) * 2 + (y >> shift & 1));
    }
}