How to get WMS LegendGraphics using Geoserver and GeoWebCache?

Question

I am using GeoServer alongwith the default, build in GeoWebCache. I am using Extjs and GeoExt, as well. Everything is running well, except for the legend graphics request. My code for layers is as follows:

var MyLayer = new OpenLayers.Layer.WMS( "MyLayer",
        "http://my-ip-address/geoserver/gwc/service/wms",
        {layers: 'MyLayer',transparent: "true",format: "image/png",
        tileSize: new OpenLayers.Size(256,256),
                tilesOrigin : map.maxExtent.left + ',' + map.maxExtent.bottom },
                { isBaseLayer: false, visibility:false} );

And for legend panel:

var legend = new GeoExt.LegendPanel({
    title: "Map Legend",
    iconCls: 'legend',
                autoScroll: true,
                defaults: {
                    cls: 'legend-item',
        baseParams: {FORMAT: 'image/png'}
                },
                items: []
            });

Whenever I am trying to open this map, I am getting the layer name in my legend panel, but there is no image for layer legend and firebug is giving this error:

"NetworkError: 400 Bad Request - http://my-ip-address/geoserver/gwc/service/wms?TRANSPARENT=true&TILESIZE=256,256&TILESORIGIN=72.45,24.45&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetLegendGraphic&EXCEPTIONS=application.ogc.se_xml&LAYER=MyLayer&FORMAT=image/gif&SCALE=2500000.0000000005&FORMAT=image/png"

I understand I will have to replace part of the URL request for GetLegendGraphic. But I am not able to do the same.Could anybody tell me how to accomplish this?

• I am using GeoServer 2.1.1; GeoWebCache 1.2.6, OpenLayers 2.11, Ext 3.2.1 and GeoExt 1.1.

Answer 1

The correct url for the legend graphic for each layer and style is embedded in the GetCapabilities response as the LegendURL element. To get it:

1. fetch the capabilities xml document
2. parse it (OpenLayers has a parser class)
3. retrieve the LegendURL for each layer you're interested in

Alternatively you can build a GetLegendGraphic request by following the documentation here.

Answer 2

Finally I am able to fetch LegendGraphic. from this post.

All I had to do is loop through all my layers, and then set the legendURL.

 var layers; 
 for(var i = 1; i < map.layers.length; i++) 
 { 
    layers; = mapPanel.layers.getAt(i);
    layers.set("legendURL","http://my-ip-address/geoserver/wms?TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetLegendGraphic&EXCEPTIONS=application%2Fvnd.ogc.se_xml&FORMAT=image%2Fpng&LAYER=" + map.layers[i].params["LAYERS"]); 
  } 

May be this will help someone else!