Reprsenting OGC services in a THREDDS catalog

• To: thredds@xxxxxxxxxxxxxxxx
• Subject: Reprsenting OGC services in a THREDDS catalog
• From: Daniel Holloway <d.holloway@xxxxxxxxxxx>
• Date: Wed, 19 Jun 2002 15:34:13 -0400

   Continuing  my autogeneration of THREDDS catalogs from
dods-dir service requests, following is an example of a catalog
representing a filesystem directory where the datafiles are
accessible from 4 different access protocols.   In particular
I'm looking for input on how to represent the OGC services for
WMS/WCS access to the datafiles.

    First, given that the OGC WMS/WCS request protocol is
well-defined, client applications expect to interrogate the
remote server for its capabilities document, and then request
the appropriate layer.  Also, layers on a WMS/WCS server
to a certain extent are an abstract representation of the
underlying data granules comprising the layer.  When I state
'abstract' I mean that only in the sense that the layer name is
an arbitrary name provided, and the multi-granular nature of
multifile data archives is represented in the layer's sample
dimensions.   To make a long story short, all a WMS/WCS
client really needs is the layer name corresponding to a
particular collection/dataset to properly access the datafile
with that service (assuming the client app interacts with the
server to determine the sample dims, etc.) (Dataset #1
in the example)

   However, if you want to insure that a particular datafile is
accessed by the WMS/WCS service, without requiring the
client to figure out the sample dimensions necessary
to access that particular datafile, then you would need to
add the minimal set of sample dimensions necessary to
uniquely identify the granule in the particular WMS/WCS
server.  (Dataset #2 in the example)

   It would be relatively easy to support example 1 in an
automated mode, and somewhat  more difficult to support
example #2.  Is example #1 sufficient?  Is it even correct
given I'm using the empty string in urlPath?

Thanks,

   Dan

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE catalog SYSTEM 
"http://www.unidata.ucar.edu/projects/THREDDS/xml/InvCatalog.0.6d.dtd";>
<catalog name="pub/ocean_wind/quikscat/L3/data/2002/" version="0.6">
  <collection name="pub/ocean_wind/quikscat/L3/data/2002/">
     <service name="DODS" serviceType="DODS" 
base="http://dods.jpl.nasa.gov/dods-bin/nph-dods/"/>
     <service name="FTP" serviceType="FTP" base="http://podaac.jpl.nasa.gov/"/>
     <service name="WCS" serviceType="WCS" 
base="http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl";>
        <property name="layer" value="QuikScat-Level3"/>
     </service>
     <service name="WMS" serviceType="WMS" 
base="http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl";>
        <property name="layer" value="QuikScat-Level3"/>
     </service>

     <dataset name="QS_XWGRD3_2002001.20020041637.Z" serviceName="DODS" 
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.Z">
        <access serviceName="FTP" serviceType="FTP" 
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.Z"/>
        <access serviceName="WCS" serviceType="WCS" urlPath=""/>
        <access serviceName="WMS" serviceType="WMS" urlPath=""/>        
     </dataset>


     <dataset name="QS_XWGRD3_2002002.20020041638.Z" serviceName="DODS" 
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041638.Z">
        <access serviceName="FTP" serviceType="FTP" 
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041638.Z"/>
        <access serviceName="WCS" serviceType="WCS" 
urlPath="?SERVICE=WCS&REQUEST=GetCoverage&TIME=2002-01-02&LAYER=QuikScat-Level3"/>
        <access serviceName="WMS" serviceType="WMS" 
urlPath="?SERVICE=WMS&REQUEST=GetMap&TIME=2002-01-02&LAYER=QuikScat-Level3"/>   
    
     </dataset>

     ...

  </collection>
</catalog>

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