[OpenLayers-Users] confused about wms projections and spherical mercator

[Andreas Hocevar]

Jonathan Wolfe wrote:
> I'm just playing with the examples here 
> (http://trac.openlayers.org/wiki/AvailableWMSServices) and can't get 
> this one to plot on a spherical mercator as it gives:
>
> msWMSLoadGetParams(): WMS Server error. Invalid SRS : SRS must be valid 
> for all selected layers.
>
> Please correct me if I'm wrong, but can't anything be reprojected onto 
> the google projection?

It can, but MapServer only offers the projections that a layer is
configured to support. To see these, just issue a GetCapabilities
request. For the server from your snippet below, this would be

http://www2.dmsolutions.ca/cgi-bin/mswms_gmap?request=GetCapabilities&service=WMS&version=1.1.1

As you can see, most layers in there are only provided in EPSG:42304.

>  It's just a reprojection, right?  Also, is 
> mapserver on a remote server? Like in this example, it would be their 
> mapserver that would need to be changed to reproject the data?
>   

Exactly.

Regards,
Andreas.

> Hopefully someone can shed some light on how these pieces fit together.
>
> Thanks,
> Jonathan
>
>
> here is the relevant snippets:
>  var options = {
>                                 projection: new 
> OpenLayers.Projection("EPSG:900913"),
>                                 displayProjection: new 
> OpenLayers.Projection("EPSG:4326"),
>                                 units: "m",
>                                 maxResolution: 156543.0339,
>                                 maxExtent: new 
> OpenLayers.Bounds(-20037508, -20037508, 20037508, 20037508.34)
>                         };
> map = new OpenLayers.Map('map', options);
>
> var dm_wms = new OpenLayers.Layer.WMS( "DM Solutions Demo",
>                 "http://www2.dmsolutions.ca/cgi-bin/mswms_gmap",
>                 {layers: "bathymetry,land_fn,park,drain_fn,drainage," +
>                          "prov_bound,fedlimit,rail,road,popplace",
>                  transparent: "true", format: "image/png" });
>
> map.addLayer(dm_wms);
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>   


-- 
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.