gmaps_mercator.js

  function Point(x, y) {
      this.x = x;
      this.y = y;
  }

  /** return a copy of this point with coordinates as int */
  Point.prototype.floor = function() {
      return new Point(this.x>>0, this.y>>0);
  }

  function LatLng(lat, lng) {
      this.lat = lat;
      this.lng = lng;
  }

  LatLng.prototype.clone = function() {
      return new LatLng(this.lat, this.lng);
  }

  var TILE_SIZE = 256;

  MercatorProjection.prototype.TILE_SIZE = TILE_SIZE;

  function bound(value, opt_min, opt_max) {
    if (opt_min != null) value = Math.max(value, opt_min);
    if (opt_max != null) value = Math.min(value, opt_max);
    return value;
  }

  function degreesToRadians(deg) {
    return deg * (Math.PI / 180);
  }

  function radiansToDegrees(rad) {
    return rad / (Math.PI / 180);
  }

  function MercatorProjection() {
    this.pixelOrigin_ = new Point(TILE_SIZE / 2,
        TILE_SIZE / 2);
    this.pixelsPerLonDegree_ = TILE_SIZE / 360;
    this.pixelsPerLonRadian_ = TILE_SIZE / (2 * Math.PI);
  }

  MercatorProjection.prototype.fromLatLngToPixel = function(latLng, zoom) {
      var p = this.fromLatLngToPoint(latLng);
      return this.toPixelCoordinate(p, zoom);
  };

  MercatorProjection.prototype.fromLatLngToPoint = function(latLng,
      opt_point) {
    var me = this;
    var point = opt_point || new Point(0, 0);
    var origin = me.pixelOrigin_;

    point.x = origin.x + latLng.lng * me.pixelsPerLonDegree_;

    // NOTE(appleton): Truncating to 0.9999 effectively limits latitude to
    // 89.189.  This is about a third of a tile past the edge of the world
    // tile.
    var siny = bound(Math.sin(degreesToRadians(latLng.lat)), -0.9999,
        0.9999);
    point.y = origin.y + 0.5 * Math.log((1 + siny) / (1 - siny)) *
        -me.pixelsPerLonRadian_;
    return point;
  };

  MercatorProjection.prototype.fromPointToLatLng = function(point) {
    var me = this;
    var origin = me.pixelOrigin_;
    var lng = (point.x - origin.x) / me.pixelsPerLonDegree_;
    var latRadians = (point.y - origin.y) / -me.pixelsPerLonRadian_;
    var lat = radiansToDegrees(2 * Math.atan(Math.exp(latRadians)) -
        Math.PI / 2);
    return new LatLng(lat, lng);
  };

  MercatorProjection.prototype.tileBBox = function(x, y, zoom) {
    var numTiles = 1 << zoom;
    var inc = TILE_SIZE/numTiles;
    var px = x*TILE_SIZE/numTiles;
    var py = y*TILE_SIZE/numTiles;
    return [
        this.fromPointToLatLng(new Point(px, py + inc)),
        this.fromPointToLatLng(new Point(px + inc, py))
    ];
  };

  MercatorProjection.prototype.tilePoint = function(x, y, zoom) {
        var numTiles = 1 << zoom;
        var px = x*TILE_SIZE;
        var py = y*TILE_SIZE;
        return [px, py];
  }

  MercatorProjection.prototype.toPixelCoordinate = function(worldCoordinate, zoom) {
        var numTiles = 1 << zoom;
        return new Point(
                worldCoordinate.x * numTiles,
                worldCoordinate.y * numTiles);
  }

  MercatorProjection.prototype.latLngToTilePoint = function(latLng, x, y, zoom) {
        var numTiles = 1 << zoom;
        var projection = this;
        var worldCoordinate = projection.fromLatLngToPoint(latLng);
        var pixelCoordinate = new Point(
                worldCoordinate.x * numTiles,
                worldCoordinate.y * numTiles);
        var tp = this.tilePoint(x, y, zoom);
        return new Point(
                Math.floor(pixelCoordinate.x - tp[0]),
                Math.floor(pixelCoordinate.y - tp[1]));
  }

  MercatorProjection.prototype.pixelToTile = function(pixelCoordinate) {
        return new Point(
                Math.floor(pixelCoordinate.x / TILE_SIZE),
                Math.floor(pixelCoordinate.y / TILE_SIZE));
  };

  MercatorProjection.prototype.pointToTile = function(point, zoom) {
        var numTiles = 1 << zoom;
        var pixelCoordinate = new Point(
                point.x * numTiles,
                point.y * numTiles);
        return this.pixelToTile(pixelCoordinate);
  };

  MercatorProjection.prototype.latLngToTile = function(latLng, zoom) {
        var numTiles = 1 << zoom;
        var projection = this;
        var worldCoordinate = projection.fromLatLngToPoint(latLng);
        var pixelCoordinate = new Point(
                worldCoordinate.x * numTiles,
                worldCoordinate.y * numTiles);
        return new Point(
                Math.floor(pixelCoordinate.x / TILE_SIZE),
                Math.floor(pixelCoordinate.y / TILE_SIZE));
  }