OpenLayers WMS - TypeError: this.resolutions is undefined

Question

I'm trying to setup a map with WMS and WFS Layers by using Geoserver. However, when I'm combining WFS and WMS (with some Google basemaps) together in one map I got following error in Firebug: TypeError: this.resolutions is undefined which is located in the http://openlayers.org/dev/OpenLayers.js JS-file Then I can see the WFS layer but not the WMS layer, furthermore also navigating in the map becomes very difficult...

The WFS Layer look like this:

       var tracks = new OpenLayers.Layer.Vector("Tracks", {
    strategies: [new OpenLayers.Strategy.BBOX()],
    styleMap: style,
    protocol: new OpenLayers.Protocol.WFS({
        version: "1.1.0",
        url: "http://localhost:8080/geoserver/wfs",
        featureNS: "http://shapes.net/shapes",
        featureType: "tracks",
        geometryName: "the_geom",
    })
});

Well, thise works quite good but as soon as I'm adding also a WMS Layer into the map i got the Error

var corine =  new OpenLayers.Layer.WMS( "OpenLayers WMS",
                "http://vmap0.tiles.osgeo.org/wms/vmap0",
                {layers: 'basic'} );

It doesn't matter if I take a WMS from my Geoserver or from an other external source (like in the code here), I always got the error when I'm activating this layer.

Btw. if the layers are not combined the works fine...

My assumption is that there could be a problem with the projection. Both layers are defined in Geoserver with EPSG:4326.

In the init.js I'm using this projects here:

projection: new OpenLayers.Projection("EPSG:4326"),
displayProjection: new OpenLayers.Projection("EPSG:900913"),

Any ideas?

Answer 1

For a wms layer, you have to specify available resolutions, i.e. zoom levels. Add this to your options object for the wms layer:

resolutions: [1.40625,0.703125,0.3515625,0.17578125,0.087890625,0.0439453125]

Note, this only covers a few zoom levels, you should google for the full resolutions array which contains 18 standard zoom levels/resolutions, or more if neccessary

Answer 2

I addition to U2ros's answer I would add srsName: "EPSG:4326", to your protocol options