Re: [thredds] future TDS WCS support for irregular/curvilinear grids?



On 6/15/2011 6:25 PM, Ben Domenico wrote:
Hi John et al.,

I am currently at the OGC Technical Committee meetings so your note is quite timely. My concept of how this sort of capability might be worked into the standards -- from the netCDF point of view anyway -- is via the CF conventions. We are currently working on a CF extension for the OGC netCDF core standard. At the same time we are working on a CF-netCDF encoding standard for WCS 2.0. But my understanding is that irregular/curvilinear grids are not formally adopted yet as part of the CF conventions. When these grids officially become part of CF, we can then do a revised extension to CF-netCDF and to WCS.

Hi Ben,

Curvilinear grids (i.e. 2D grids where latitude and longitude coordinates are themselves 2D fields defined on the i,j index space) have been supported by CF for many years. In fact, time-dependent and 3D generalizations of these are also supported by CF. It is the "gridspec" (multi-tile mosaic) generalizations of these concepts that are brand new. Coincidentally, the CF extensions became formally part of CF just a couple of weeks ago. Following an editing delay, they will be visible in the on-line CF documents.

    - Steve


Please correct me if I'm wrong about the status of irregular/curvilinear grids in CF. If you have suggestions for better ways to accomplish this, let me know. But for now this is the general outline of the plan for getting this into the formal standards world.

For what it's worth.
-- Ben

On Wed, Jun 15, 2011 at 6:23 PM, John Maurer <jmaurer@xxxxxxxxxx <mailto:jmaurer@xxxxxxxxxx>> wrote:

    Thanks for the explanation, Ethan. If TDS could handle the
    regridding itself, then it could work. I assume this is what's
    happening on the backend via TDS/ncWMS for GetMap requests since
    the WMS spec doesn't handle irregular/curvilinear grids either
    (right?). I was hoping a future enhancement could someday do the
    same for TDS WCS. Something for the suggestion box.
    Cheers,
    John


    On Wed, Jun 15, 2011 at 2:17 PM, Ethan Davis
    <edavis@xxxxxxxxxxxxxxxx <mailto:edavis@xxxxxxxxxxxxxxxx>> wrote:

        Hi John,

        TDS currently only supports WCS 1.0.0. The WCS 1.0.0 specification
        itself does not support requesting or returning
        irregular/curvilinear
        grids. I believe the same is true for WCS 1.1.0.

        I don't belive this is necessarily the case for WCS 2.0.
        However, the
        2.0 specification is written in the new core/extensions
        paradigm and I
        don't believe the extensions necessary to request or return
        irregular/curvilinear grids are yet written.

        The TDS WCS implementation does not currently support
        regridding data.
        So, currently one gets the data from the WCS in the same
        projection in
        which the data is stored. The combination means the TDS WCS
        can only
        serve regularly gridded data.

        Ethan

        On 6/15/2011 5:31 PM, John Maurer wrote:
        > Hi All,
        > We now use the WCS service through TDS to serve GeoTIFF
        files to users.
        > Since it only works for regular grids, I was wondering if
        TDS could be
        > enhanced in the future to support irregular/curvilinear
        grids via WCS?
        > TDS/ncWMS already handles curvilinear grids via WMS, so I
        was hoping the
        > same sort of intervening magic could be applied for TDS' WCS
        service?
        > Thoughts?
        > Thanks for listening!,
        > John Maurer
        > Pacific Islands Ocean Observing System (PacIOOS)
        > University of Hawaii at Manoa

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