[OSM-dev] strange OpenLayers longitude and latitude

Thu Aug 30 18:20:37 BST 2007

OSM tiles are projected. Displaying them in an unprojected map will not
work at all how you expect. 

-- Chris

On Thu, Aug 30, 2007 at 09:06:58PM +0400, Vladimir Elistratov wrote:
> Hi!
> 
> I added the option to see the longitude and latitude for the TMS Layer 
> http://tile.openstreetmap.org
> It is well known line:
> map.addControl(new OpenLayers.Control.MousePosition());
> 
> The longitude and latitude seem to be quite strange. Say, the 
> longitude for London is around 90.
> 
> What is the problem about! How is it possible to get "normal" 
> longitude and latitude?
> 
> I attach the small file for you to see how it happens.
> 
> The related Javascript code:
>     <script type="text/javascript">
>         var lon = 90;
>         var lat = 29;
>         var zoom = 6;
>         var map, layer;
> 
>         function init(){
>             map = new OpenLayers.Map( 'map', 
> {maxResolution:1.40625/2} );
> 
> 		var mapnik = new OpenLayers.Layer.TMS("Mapnik", 
> "http://tile.openstreetmap.org/",
>                                          { type: 'png', getURL: 
> getTileURL, displayOutsideMaxExtent: true });
> 
>             map.addLayer(mapnik);
> 
>             map.addControl(new OpenLayers.Control.LayerSwitcher());
> 		map.addControl(new OpenLayers.Control.MousePosition());
>             map.setCenter(new OpenLayers.LonLat(lon, lat), zoom);
>         }
> 
> 	function getTileURL(bounds) {
> 		var res = this.map.getResolution();
> 		var x = Math.round((bounds.left - this.maxExtent.left) / 
> 		(res * this.tileSize.w));
> 		var y = Math.round((this.maxExtent.top - bounds.top) / (res 
> 		* this.tileSize.h));
>    		var z = this.map.getZoom();
> 		var limit = Math.pow(2, z);
> 
> 		if (y < 0 || y >= limit)
> 		{
> 			return OpenLayers.Util.getImagesLocation() + 
> 			"404.png";
>    		}
> 		else
> 		{
> 			x = ((x % limit) + limit) % limit;
> 			return this.url + z + "/" + x + "/" + y + "." + 
> 			this.type;
> 		}
> 	}
> 
>     </script>
> 
> Thank you for any advice!
> 

> <html xmlns="http://www.w3.org/1999/xhtml">
>   <head>
> 
>     <script src="http://www.openlayers.org/api/OpenLayers.js"></script>
>     <script type="text/javascript">
>         var lon = 90;
>         var lat = 29;
>         var zoom = 6;
>         var map, layer;
> 
>         function init(){
>             map = new OpenLayers.Map( 'map', {maxResolution:1.40625/2} );
> 
> 		var mapnik = new OpenLayers.Layer.TMS("Mapnik", "http://tile.openstreetmap.org/",
>                                          { type: 'png', getURL: getTileURL, displayOutsideMaxExtent: true });
> 
>             map.addLayer(mapnik);
> 
>             map.addControl(new OpenLayers.Control.LayerSwitcher());
> 		map.addControl(new OpenLayers.Control.MousePosition());
>             map.setCenter(new OpenLayers.LonLat(lon, lat), zoom);
>         }
> 
> 	function getTileURL(bounds) {
> 		var res = this.map.getResolution();
> 		var x = Math.round((bounds.left - this.maxExtent.left) / (res * this.tileSize.w));
> 		var y = Math.round((this.maxExtent.top - bounds.top) / (res * this.tileSize.h));
>    		var z = this.map.getZoom();
> 		var limit = Math.pow(2, z);
> 
> 		if (y < 0 || y >= limit)
> 		{
> 			return OpenLayers.Util.getImagesLocation() + "404.png";
>    		}
> 		else
> 		{
> 			x = ((x % limit) + limit) % limit;
> 			return this.url + z + "/" + x + "/" + y + "." + this.type;
> 		}
> 	}  
> 
>     </script>
>   </head>
>   <body onload="init()">
>     <div id="map"></div>
>   </body>
> </html>

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-- 
Christopher Schmidt
MetaCarta