[Users] Problem showing WMS in Mercator projection

Tue Feb 15 10:59:27 CET 2011

Hi, 

I am trying to combine WMS-layers with the Openstreet Map as background. 
The WMS-layers disapear as soon as I zoom in. 
When working in geographic projection, I manage to get the WMS to show on a background layer. 
I know it is possible as in the opengeo suite, it is possible to do it. Unfortunately, I cannot see how they did it. 
I have added two simple examples with layers available on the net and the javascripts refering to the online sources. 

Can somebody explain me what I do wrong? 

A working simple example with the default projection: 
==================================== 
<html> 
<head> 

<title> A working GeoExt Map </title> 
<script src="http://extjs.cachefly.net/ext-3.2.1/adapter/ext/ext-base.js" type="text/javascript"></script> 
<script src="http://extjs.cachefly.net/ext-3.2.1/ext-all.js" type="text/javascript"></script> 
<link rel="stylesheet" type="text/css" href="http://extjs.cachefly.net/ext-3.2.1/resources/css/ext-all.css"></link> 
<script src="http://openlayers.org/api/OpenLayers.js" type="text/javascript"></script> 
<script src="http://api.geoext.org/1.0/script/GeoExt.js" type="text/javascript"></script> 
<link rel="stylesheet" type="text/css" href="http://api.geoext.org/1.0/resources/css/geoext-all-debug.css"></link> 

<script type="text/javascript"> 
Ext.onReady(function() { 

var map = new OpenLayers.Map({allOverlays: true}); 
var kansas = new OpenLayers.LonLat(-99, 39); 

var usa = new OpenLayers.Layer.WMS( 
"usa", "http://demo.opengeo.org/geoserver/wms", 
{ 
height: '330', 
width: '680', 
layers: 'nurc:Img_Sample', 
styles: '', 
srs: 'EPSG:4326', 
format: 'image/png' 
}, 
{singleTile: true, ratio: 1} 
); 
var layer = new OpenLayers.Layer.WMS( 
"USA pop", 
"http://demo.opengeo.org/geoserver/wms", 
{layers: "topp:states"}, 
{opacity: 0.5} 
); 

map.addLayer(usa); 
map.addLayer(layer); 

new GeoExt.MapPanel({ 
renderTo: 'gxmap', 
height: 400, 
width: 600, 
map: map, 
center: kansas, 
zoom: 4, 
title: 'A working GeoExt Map, default projection' 
}); 
}); 
</script> 
</head> 
<body> 
<div id="gxmap"></div> 
</body> 
</html> 

============================================ 
the not working example with mercator projection 
============================================ 

<html> 
<head> 

<title> A WMS failing GeoExt Map </title> 
<script src="http://extjs.cachefly.net/ext-3.2.1/adapter/ext/ext-base.js" type="text/javascript"></script> 
<script src="http://extjs.cachefly.net/ext-3.2.1/ext-all.js" type="text/javascript"></script> 
<link rel="stylesheet" type="text/css" href="http://extjs.cachefly.net/ext-3.2.1/resources/css/ext-all.css"></link> 
<script src="http://openlayers.org/api/OpenLayers.js" type="text/javascript"></script> 
<script src="http://api.geoext.org/1.0/script/GeoExt.js" type="text/javascript"></script> 
<link rel="stylesheet" type="text/css" href="http://api.geoext.org/1.0/resources/css/geoext-all-debug.css"></link> 

<script type="text/javascript"> 
Ext.onReady(function() { 

var geographic = new OpenLayers.Projection("EPSG:4326"); 
var mercator = new OpenLayers.Projection("EPSG:900913"); 

var map = new OpenLayers.Map({allOverlays: true, 
projection: "EPSG:900913", 
units: "m" 
}); 
var kansas = new OpenLayers.LonLat(-99, 39).transform(geographic, mercator); 

var osm = new OpenLayers.Layer.OSM(); 
var layer = new OpenLayers.Layer.WMS( 
"USA pop", 
"http://demo.opengeo.org/geoserver/wms", 
{layers: "topp:states"}, 
{opacity: 0.5} 
); 

map.addLayer(osm); 
map.addLayer(layer); 

new GeoExt.MapPanel({ 
renderTo: 'gxmap', 
height: 400, 
width: 600, 
map: map, 
center: kansas, 
zoom: 4, 
title: 'A WMS failing GeoExt Map, Mercator projection' 
}); 
}); 
</script> 
</head> 
<body> 
<div id="gxmap"></div> 
</body> 
</html> 

Erwin Sevens | OVAM 
http://www.ovam.be 

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