OpenLayers, how compute the tile "name" under the mouse

01 January, 2013 - 1 min read

I have working on a web page using OpenLayers which among others shows a  OpenStreetMap layer. The issue is I need to move the mouse over the map and print on a label the tile name  in the form of z/x/y, for example, 5/15/10.

The approach to done this is:

  1. register a listener to the OpenLayers map instance and then, for every mouse event triggered,
  2. get the lonlat and translate it from current map projection to the EPSG:4326 (WGS84).


map.events.register( 'mousemove', this, function(evt){
	var lonlat = new OpenLayers.LonLat(0, 0);
		lonlat = map.getLonLatFromPixel(evt.xy);
		lonlat.transform(this.map.getProjectionObject(), newOpenLayers. Projection("EPSG:4326") );
	tileX = long2tile(lonlat.lon, map.getZoom());
	tileY = latg2tile(lonlat.lat, map.getZoom());
	tileZ = map.getZoom();
// Print the tilez, tilex and tiley values


To compute the tile X,Y grid coordinate from latlon you can use next functions (obtained from OpenStreetMaps site):


// Functions to compute tiles from lat/lon
function long2tile(lon,zoom) {
	return (Math.floor((lon+180)/360*Math.pow(2,zoom)));
function lat2tile(lat,zoom)  {
	return (Math.floor((1-Math.log(Math.tan(lat*Math.PI/180) + 1/Math.cos(lat*Math.PI/180))/Math.PI)/2 *Math.pow(2,zoom)));
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