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Web Map Service



 
----- Original Message -----
From: "Jeff de La Beaujardiere" <address@hidden>
To: <address@hidden>
Sent: Thursday, May 16, 2002 10:52 AM
Subject: Re: New Catalog XML Draft

>
> # John Caron wrote:
> # > c.. add new service types: (DODS | ADDE | NetCDF | Catalog | FTP
> # >         | OpenGIS | WSDL | Other) .
>
> I agree that instead of OpenGIS you need explicit WMS, WFS, etc.
>
> Joe Wielgosz writes:
> # How much effort should THREDDS put into supporting particular data
> # provider site layouts?
> # [...]
> # If you look at different data providers websites, they all have their
> # own way of mapping datasets, collections and access methods to URLS, and
> # some are quite complex. They might use any combination of different base
> # URLs, subpaths or suffixes, CGI parameters, or who knows what else.
>
> The OpenGIS services (e.g., Web Map Service--WMS) list a URL prefix for
> each operation supported by a particular machine. The prefix includes
> hostname and, as needed, port number, path, and some CGI parameters.
> The entire prefix is just an opaque string. Then, the specification
> says what parameters are to be added to the prefix in order to
> construct a valid request for each operation.
>
> Examples for WMS:
>
> URL prefix:
>
http://globe.digitalearth.gov/viz-bin/wmt.cgi
>
> Complete URL to request service metadata:
>
http://globe.digitalearth.gov/viz-bin/wmt.cgi?request=GetCapabilities
>
> Complete URL to request a particular map:
>
http://globe.digitalearth.gov/viz-bin/wmt.cgi?request=GetMap&layers=RTOPO&styles=REFPIXEL&srs=EPSG:4326&bbox=-180,-90,180,90&width=512&height=256&format=image/gif
>
> In the last example showing the GetMap request, most of the parameters
> are variable. I'm not sure whether in the THREDDS catalog it is best
> to include only the URL prefix and let the client form a valid GetMap
> request, or include one of the possible complete GetMap URLs so that
> all clients can at least retrieve something while WMS-aware clients
> can modify the URL. Probably the second, more helpful option is best
> in this context.
>
> -Jeff DLB, WMS 1.1 Editor
Thanks for the concrete example (nice picture, too!). A few questions:
 
Can one figure out all the possible parameter values from the WMT_MS_Capabilities document?
Does the WMS spec allow the client to specify the projection ?
In the specific example above of the topo map, can the client specify/discover what the false color mapping is?

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