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

Hi John,


Is the current THREDDS able to handle the triangular grid through OPeNDAP
and WMS?







From: thredds-bounces@xxxxxxxxxxxxxxxx
[mailto:thredds-bounces@xxxxxxxxxxxxxxxx] On Behalf Of john caron
Sent: Wednesday, June 15, 2011 11:00 PM
To: thredds@xxxxxxxxxxxxxxxx
Subject: Re: [thredds] future TDS WCS support forirregular/curvilinear


some terms as far as i understand:

regular grids:                    1d x, y coordinates evenly spaced. only
ones WCS 1.0 allows
irregularly spaced grids:  1d x,y, but dont have to be even, eg gaussian
curvilinear grids:                2d x,y but each section is a quadilateral
and connected to its neighbor (implicit topology)

CF allows both irregular and curvilinear grids. one could extend WCS to
return netcdf/CF irregular and curvilinear grids, without regridding.

unstructured grids: arbitrary meshes, explicit topology, no CF standard yet.

John, why do you want WCS? To get geotiffs, or ?? 

On 6/15/2011 7:25 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.


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> 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.


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

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.


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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