WFS not in position when using a Google Base Layer

Question

I use two base layers and user can switch from OSM MapQuest to Google from a drop down list. However my WFS layer is not in position (shift of about 5 degrees to the East) when the base layers is a Google Base Layer. Position is fine when the OSM layer is used.

I have read a few posts about related problems which were caused by wrong coordinate systems for the map (not using spherical Mercator for the map projection) but I tried to set it properly.

    geographic = new OpenLayers.Projection("EPSG:4326");
    mercator = new OpenLayers.Projection("EPSG:3857");

    OLmap = new OpenLayers.Map('map', {

        projection: mercator,
        //maxExtent: extent,

        controls: [
            new OpenLayers.Control.Navigation(),
            new OpenLayers.Control.MousePosition(), //{div:document.getElementById("coordinates")}
            new OpenLayers.Control.ScaleLine(),
            new OpenLayers.Control.Zoom()           
        ],
        zoomDuration: 2,
        numZoomLevels: 10,
        displayProjection: geographic
    });

    arrayOSM = ["http://otile1.mqcdn.com/tiles/1.0.0/map/${z}/${x}/${y}.jpg",
                "http://otile2.mqcdn.com/tiles/1.0.0/map/${z}/${x}/${y}.jpg",
                "http://otile3.mqcdn.com/tiles/1.0.0/map/${z}/${x}/${y}.jpg",
                "http://otile4.mqcdn.com/tiles/1.0.0/map/${z}/${x}/${y}.jpg"];

    baseOSM = new OpenLayers.Layer.OSM("Political map", arrayOSM,OpenLayers.Layer.OSM,
        {'maxExtent': new OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34)});
    OLmap.addLayer(baseOSM);

    var gphy = new OpenLayers.Layer.Google(
        "Google Physical",
        {type: google.maps.MapTypeId.TERRAIN}
        // used to be {type: G_PHYSICAL_MAP}
    );  

    OLmap.addLayer(gphy);

    Feature_centroid_wfs = new OpenLayers.Layer.Vector("site",
    {
        projection: geographic // layers' original projection
        ,styleMap: StyleObject
        ,rendererOptions: {zIndexing: true}
        ,strategies: [new OpenLayers.Strategy.Fixed()]          
        ,protocol: new OpenLayers.Protocol.WFS({
            version: "1.1.0"
            ,url: "http://myserver/geoserver/wfs"
            ,featurePrefix: "ramsar_sdi" //geoserver worspace name
            ,featureType: "features_centroid_published" //geoserver Layer Name
            ,featureNS: "http://myserver/geoserver/ramsar_sdi" // Workspace URI
            ,geometryName: "geom" // field in Feature Type details with type "Geometry"
            ,srsName : "EPSG:4326" 
            ,outputFormat: "application/json"
            ,readFormat: new OpenLayers.Format.GeoJSON()
            //,maxExtent: extent  // necessary if BBOX()
        })
    });

    OLmap.addLayer(Feature_centroid_wfs);

Answer 1

Your projection value should be a String.

Change mercator to

mercator = "EPSG:3857";

And Just to be clear: You are setting the displayProjection correctly as it requires an OpenLayers.Projection object. It's just the projection value that should be a String.