WMS and SRS

[Trond Michelsen]

On Thu, Jul 27, 2006 at 09:04:39AM +0200, Daniel Goetz wrote:

> I built up a littel WMS-server with umn-mapserver (local
> installation; ms4w 2.1). The "original" projection of the single
> Layers is alway epsg:31468 (these are cartesian
> Gauß-Krüger-coordiantes). So I set the PORJECTION-object of each
> LAYER and in the MAP-object to "init=epsg:31468". In the METADATA of
> the MAP-object as well as in the single LAYER-objects I defined
> "wms_srs" as "EPSG:31468" as well. For testing purpose I did some
> WMS-GetMap-Requests with "SRS=EPSG:31468" and everything went fine.

> But now I want to make my WMS-service more interchangeable, so I
> want to define some more SRSs in that the WMS should be able to be
> displayed. I want to make it possible to "transform" (don't know the
> exact word in english) the WMS from its original Projection to
> another SRS (e.g. WGS 84; EPSG:4326). In my opinion this should be
> possible by adding another epsg-code to the METADATA. So my METADATA
> (both in the MAP and in the LAYERs-objects) look like this:
> "wms_srs" "EPSG:31468 EPSG:4326".

I'm struggling a bit to grok projections myself, but if I understood
your question properly, you should remove EPSG:4326 from the metadata
of the individual layers. As I understood it, every layer is _always_
in EPSG:31468, and you want to display them in EPSG:4326. If you
include EPSG:4326 in the layers' metadata, then mapserver will think
it's OK to request that layer with EPSG:4326, when it probably isn't.

When you remove EPSG:4326 from the layers' metadata, mapserver will
fetch the layer with EPSG:31468 as the projection, then reproject it
to EPSG:4326

-- 
Trond Michelsen