[Mapserver-dev] WMS and LAYERS= vs. STATUS Behaviour

[Daniel Morissette]

Frank Warmerdam wrote:
> 
> It seems that a layer with STATUS DEFAULT will be returned in a GetMap
> request against MapServer regardless of whether the layer is in the
> layers list or not.  Is this the expected behaviour?
> 

This is the expected behavior, which is in line with the behavior of the 
original mapserv CGI in which layers with status default cannot be 
turned off.


> 
> I would have hoped MapServer would have:
>  o returned only the requested layers if there is a LAYERS= parameter
>    in the WMS GetMap request.

I think that's what we used to do in very early versions of MapServer, 
but we changed at some point (way back when, in v3.5 or so) to handle 
the STATUS DEFAULT the same way in WMS as in the mapserv CGI.

This also allows things like putting a copyright notice or a watermark 
which cannot be removed by the caller (I'm not saying it's a good idea 
to do so because it breaks WMS-based apps, but the software allows it 
inthe WMS interface the same way as with the traditional CGI)


>  o Returned only STATUS DEFAULT layers if there was no LAYERS= parameter
>    in the WMS GetMap request.
> 

This is contrary to the WMS spec.  We used to return all layers with 
STATUS ON or DEFAULT when LAYERS wasn't specified, but when we ran the 
CITE test suite we had to change v4.1 to produce an exception if LAYERS= 
parameter is missing. (This is annoying but is required in order to 
follow the spec: the LAYERS= parameter is required and must contain 
valid layer names)

> If things are behaving as intended, then I think the WMS Server HOWTO
> should mention this gotcha.
> 

We should update the docs then... I have filed a bug about this:
http://mapserver.gis.umn.edu/bugs/show_bug.cgi?id=636

Daniel
-- 
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  Daniel Morissette               dmorissette at dmsolutions.ca
  DM Solutions Group              http://www.dmsolutions.ca/
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