Difficulty to display WMS and Googlemaps layers using Geoext and ext

Question

i have the following code on my html file:

        // World Geodetic System 1984 projection
    var WGS84 = new OpenLayers.Projection("EPSG:4326");

    // WGS84 Google Mercator projection
    var WGS84_google_mercator = new OpenLayers.Projection("EPSG:900913");       


    // create a map panel with some layers that we will show in our layer tree
    // below.
    layers = [];

    layers.push(new OpenLayers.Layer.Google("Google Maps", {
        numZoomLevels: 20
                    , 'sphericalMercator' : true
            }
    ));

    layers.push(new OpenLayers.Layer.WMS(
    "National Parks", "http://localhost:8080/geoserver/wms", {
        srs: 'EPSG:4326',
        layers: 'National_Parks',
        format: 'image/png',
        buffer:0
    }, {
        'isBaseLayer': false
    }
    ));

    map = new OpenLayers.Map({
        allOverlays: false  // If it is true then both the wms and the map layers will be included under the "Overlays" folder

    });

    mapPanel = new GeoExt.MapPanel({
        region: "center",
        center: new OpenLayers.Bounds(-16.08,49.06,6.76,58.74).transform(WGS84, map.getProjectionObject()),
        zoom: 2,
        map: map
    });

    map.addLayers(layers);

As the code is at the moment i can see the googlemaps layer at full extent (although i wanted it zoomed in at these boundaries -16.08,49.06,6.76,58.74) but i can not see the national parks wms layer.

What i did was to add 'displayOutsideMaxExtent':true next to 'isBaseLayer': false on the wms properties. When i did that i could see tha wms layer on all zoom levels but i couldnt see googlemaps at all. when i was zooming in and out the googlemaps layer was appearing instantly and then it was going off.

Does anyone have any idea where the problem might be?

I am using Geoserver, Openlayers, GeoExt and ext.

Thanks

Answer 1

For safety you should explicitly set the map projection, otherwise the projection of the first layer is used and it's not clear which of those layers will end up first.

Your code is also assuming that the WMS server can reproject for you - it probably can but that could also be the problem. Check what it is returning using firebug (this will also allow you to check what SRS is being sent as OpenLayers will ignore the SRS you set in the WMS layer.

Answer 2

Is a projection issue.

You have in the layer properties 2 parameters, projection and displayProjection, projection is for the projection of the source, displayProjection is for reproject to "that" projection, now OpenLayers could reproject only vector Layers, because OpenLayers render it, but OpenLayers cannot reproject a image layer.

So you have to reproject in the geoserver side. If you have reproject function in geoserver side you just need to pass to the map projection parameter the spherical mercator projection, because google will not reproject (is little ovbious).

OpenLayers docs about reprojection and tips to use Spherical mercator.

http://docs.openlayers.org/library/spherical_mercator.html

http://trac.osgeo.org/openlayers/wiki/SphericalMercator

Answer 3

Set transparent : True.

layers.push(new OpenLayers.Layer.WMS(
        "National Parks", "http://localhost:8080/geoserver/wms", {
            srs: 'EPSG:4326',
            layers: 'National_Parks',
            format: 'image/png',
            transparent: true,
            buffer:0
        }, {
            'isBaseLayer': false
        }
        ));