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Re: New Catalog XML Draft

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  • Subject: Re: New Catalog XML Draft
  • Date: Thu, 16 May 2002 12:52:22 -0400 (EDT)
# 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


       Dr. Jeff de La Beaujardiere * Computer Scientist
           NASA Geographic Interoperability Office
            Goddard Space Flight Center * Code 933
       address@hidden * +1 301 286 1569
                http://sunrise.gsfc.nasa.gov/