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<!DOCTYPE html>
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<html>
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<head>
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<title>Showing pixel and tile coordinates</title>
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<meta name="viewport" content="initial-scale=1.0, user-scalable=no">
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<meta charset="utf-8">
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<link href="/maps/documentation/javascript/examples/default.css" rel="stylesheet">
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<script src="https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false"></script>
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<script>
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var map;
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var TILE_SIZE = 256;
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var chicago = new google.maps.LatLng(41.850033,-87.6500523);
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function bound(value, opt_min, opt_max) {
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if (opt_min != null) value = Math.max(value, opt_min);
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if (opt_max != null) value = Math.min(value, opt_max);
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return value;
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}
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function degreesToRadians(deg) {
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return deg * (Math.PI / 180);
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}
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function radiansToDegrees(rad) {
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return rad / (Math.PI / 180);
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}
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/** @constructor */
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function MercatorProjection() {
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this.pixelOrigin_ = new google.maps.Point(TILE_SIZE / 2,
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TILE_SIZE / 2);
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this.pixelsPerLonDegree_ = TILE_SIZE / 360;
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this.pixelsPerLonRadian_ = TILE_SIZE / (2 * Math.PI);
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}
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MercatorProjection.prototype.fromLatLngToPoint = function(latLng,
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opt_point) {
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var me = this;
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var point = opt_point || new google.maps.Point(0, 0);
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var origin = me.pixelOrigin_;
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point.x = origin.x + latLng.lng() * me.pixelsPerLonDegree_;
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// Truncating to 0.9999 effectively limits latitude to 89.189. This is
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// about a third of a tile past the edge of the world tile.
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var siny = bound(Math.sin(degreesToRadians(latLng.lat())), -0.9999,
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0.9999);
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point.y = origin.y + 0.5 * Math.log((1 + siny) / (1 - siny)) *
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-me.pixelsPerLonRadian_;
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return point;
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};
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MercatorProjection.prototype.fromPointToLatLng = function(point) {
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var me = this;
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var origin = me.pixelOrigin_;
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var lng = (point.x - origin.x) / me.pixelsPerLonDegree_;
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var latRadians = (point.y - origin.y) / -me.pixelsPerLonRadian_;
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var lat = radiansToDegrees(2 * Math.atan(Math.exp(latRadians)) -
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Math.PI / 2);
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return new google.maps.LatLng(lat, lng);
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};
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function createInfoWindowContent() {
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var numTiles = 1 << map.getZoom();
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var projection = new MercatorProjection();
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var worldCoordinate = projection.fromLatLngToPoint(chicago);
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var pixelCoordinate = new google.maps.Point(
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worldCoordinate.x * numTiles,
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worldCoordinate.y * numTiles);
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var tileCoordinate = new google.maps.Point(
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Math.floor(pixelCoordinate.x / TILE_SIZE),
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Math.floor(pixelCoordinate.y / TILE_SIZE));
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return [
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'Chicago, IL',
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'LatLng: ' + chicago.lat() + ' , ' + chicago.lng(),
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'World Coordinate: ' + worldCoordinate.x + ' , ' +
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worldCoordinate.y,
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'Pixel Coordinate: ' + Math.floor(pixelCoordinate.x) + ' , ' +
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Math.floor(pixelCoordinate.y),
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'Tile Coordinate: ' + tileCoordinate.x + ' , ' +
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tileCoordinate.y + ' at Zoom Level: ' + map.getZoom()
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].join('<br>');
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}
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function initialize() {
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var mapOptions = {
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zoom: 3,
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center: chicago,
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mapTypeId: google.maps.MapTypeId.ROADMAP
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};
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map = new google.maps.Map(document.getElementById('map-canvas'),
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mapOptions);
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var coordInfoWindow = new google.maps.InfoWindow();
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coordInfoWindow.setContent(createInfoWindowContent());
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coordInfoWindow.setPosition(chicago);
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coordInfoWindow.open(map);
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google.maps.event.addListener(map, 'zoom_changed', function() {
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coordInfoWindow.setContent(createInfoWindowContent());
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coordInfoWindow.open(map);
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});
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}
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google.maps.event.addDomListener(window, 'load', initialize);
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</script>
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</head>
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<body>
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<div id="map-canvas"></div>
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</body>
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</html>
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