[OSGeo-Standards] WMS-C and Capabilities

Andrea Aime aaime at opengeo.org
Tue Aug 26 11:19:06 EDT 2008

Christopher Schmidt ha scritto:
> On Tue, Aug 26, 2008 at 10:36:37AM +0200, Andrea Aime wrote:
>> Jody Garnett ha scritto:
>>> Just a quick confirmation; the WMS-C page here:
>>> - http://wiki.osgeo.org/wiki/WMS_Tiling_Client_Recommendation
>>> Has confused a couple implementations; my understanding is this 
>>> specification talks about adding to the VendorSpecificCapabilities of an 
>>> existing WMS server a section describing the available TileSets.
>>> Can we change the "Example VendorSpecificCapabilities" to make it really 
>>> obvious what is expected...right now I have servers returning:
>>> http://sigma.openplans.org/geowebcache/service/wms?request=getcapabilities
>>>> <WMT_MS_Capabilities version="1.1.1" updateSequence="0">
>>>>   <VendorSpecificCapabilities>
>>>>     <TileSet><SRS>EPSG:4326</SRS><BoundingBox srs="EPSG:4326" 
>>>> minx="-180.0" miny="-90.0" maxx="180.0" maxy="90.0" />
>>>>        ....
>>>>     </TileSet>
>>>>   </VendorSpecificCapabilities>
>>>> </WMT_MS_Capabilities>
>>> Which is not enough information for clients (ie uDig) to fetch Titles 
>>> and Layer information. WMS-C is not a standalone server; it is an 
>>> additional ability added to an existing WMS server.
>> Hum, reality seems to think otherwise, both TileCache and GWC are
>> born as standalone servers, they cannot serve non tiled requests.
>> GWC can be embedded in GeoServer as a convenience, but it does not
>> act as an extension to WMS.
> Reality or not, the Capabilities were designed to be in addition to
> standard WMS capabilties. The fact that TileCache doesn't do non-tiled
> requests doesn't mean that the WMS information isn't neccesary: most of
> the metadata was always supposed to be delivered by the 'traditional'
> WMS GetCaps, and excluding it from your response is (imho) buggy.
> (I don't *think* TileCache does that, but if it does, it should be
> fixed.)

I did not explain myself. I do not mean to say the capabilities document
should be partial or anything, I just mean the client cannot expect
a tiling server to answer any kind of request like a WMS would do.
The capabilities document is an extension all right, but the behaviour
is a restriction, only certain GetMap requests will be answered, no?
Put in other words, the caps document is based on WMS, but the tiling
server is not a valid WMS server, right?


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