MercatorTileSystem.java

package com.mutu.mapapi.tilesystem;

/*
 * http://msdn.microsoft.com/en-us/library/bb259689.aspx
 *
 * Copyright (c) 2006-2009 Microsoft Corporation.  All rights reserved.
 *
 *
 */

import com.mutu.mapapi.util.GeoPoint;

import android.graphics.Point;

/**
 * This class provides methods to handle the Mercator projection that is used for the osmdroid tile
 * system.
 */
public final class MercatorTileSystem extends TileSystem{


	public MercatorTileSystem(){
		EarthRadius = 6378137;
		MinLatitude = -85.05112878;;
		MaxLatitude = 85.05112878;
		MinLongitude = -180;
		MaxLongitude = 180;
	}

	public String name(){
		return "Mercator";
	}
	
	public int MapWidthPixelSize(final int levelOfDetail) {
		return mTileSize << levelOfDetail;
	}

	public int MapHeigthPixelSize(final int levelOfDetail) {
		return mTileSize << levelOfDetail;
	}
	
	public int MapWidthTileSize(final int levelOfDetail) {
		return 1 << levelOfDetail;
	}

	public int MapHeigthTileSize(final int levelOfDetail) {
		return 1 << levelOfDetail;
	}
	/**
	 * Converts a point from latitude/longitude WGS-84 coordinates (in degrees) into pixel XY
	 * coordinates at a specified level of detail.
	 * 
	 * @param latitude
	 *            Latitude of the point, in degrees
	 * @param longitude
	 *            Longitude of the point, in degrees
	 * @param levelOfDetail
	 *            Level of detail, from 1 (lowest detail) to 23 (highest detail)
	 * @param reuse
	 *            An optional Point to be recycled, or null to create a new one automatically
	 * @return Output parameter receiving the X and Y coordinates in pixels
	 */
	public Point LatLongToPixelXY(double latitude, double longitude,
			final int levelOfDetail, final Point reuse) {
		final Point out = (reuse == null ? new Point() : reuse);

		latitude = Clip(latitude, MinLatitude, MaxLatitude);
		longitude = Clip(longitude, MinLongitude, MaxLongitude);

		final double x = (longitude + 180) / 360;
		final double sinLatitude = Math.sin(latitude * Math.PI / 180);
		final double y = 0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);

		final int mapWidthPixelSize = MapWidthPixelSize(levelOfDetail);
		final int mapHeigthPixelSize = MapHeigthPixelSize(levelOfDetail);
		
		out.x = (int) Clip(x * mapWidthPixelSize + 0.5, 0, mapWidthPixelSize - 1);
		out.y = (int) Clip(y * mapHeigthPixelSize + 0.5, 0, mapHeigthPixelSize - 1);
		return out;
	}

	/**
	 * Converts a pixel from pixel XY coordinates at a specified level of detail into
	 * latitude/longitude WGS-84 coordinates (in degrees).
	 * 
	 * @param pixelX
	 *            X coordinate of the point, in pixels
	 * @param pixelY
	 *            Y coordinate of the point, in pixels
	 * @param levelOfDetail
	 *            Level of detail, from 1 (lowest detail) to 23 (highest detail)
	 * @param reuse
	 *            An optional GeoPoint to be recycled, or null to create a new one automatically
	 * @return Output parameter receiving the latitude and longitude in degrees.
	 */
	public GeoPoint PixelXYToLatLong(final int pixelX, final int pixelY,
			final int levelOfDetail, final GeoPoint reuse) {
		final GeoPoint out = (reuse == null ? new GeoPoint(0, 0) : reuse);

		final double mapWidthPixelSize = MapWidthPixelSize(levelOfDetail);
		final double mapHeigthPixelSize = MapHeigthPixelSize(levelOfDetail);
		
		final double x = (Clip(pixelX, 0, mapWidthPixelSize - 1) / mapWidthPixelSize) - 0.5;
		final double y = 0.5 - (Clip(pixelY, 0, mapHeigthPixelSize - 1) / mapHeigthPixelSize);

		final double latitude = 90 - 360 * Math.atan(Math.exp(-y * 2 * Math.PI)) / Math.PI;
		final double longitude = 360 * x;

		out.setLatitudeE6((int) (latitude * 1E6));
		out.setLongitudeE6((int) (longitude * 1E6));
		return out;
	}
}