Re: [thredds] HDF5 Aggregation

• To: "David Robertson" <robertson@xxxxxxxxxxxxxxxxxx>
• Subject: Re: [thredds] HDF5 Aggregation
• From: "Rich Signell" <rsignell@xxxxxxxx>
• Date: Fri, 30 May 2008 09:37:12 -0400

Dave,

I've been working on a similar problem:  using NcML to make the HDF
remote sensing imagery served by the NOAA Coastwatch East Coast
OpenDAP server CF-compliant.

I have been using aggregation type="union" to join the HDF data with a
netcdf file that contains the lon/lat values, since Coastwatch uses
the same non-uniform lon/lat grid (it's a uniform mercator grid).

The NcML looks like this:

<netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2";>
    <aggregation type="union">
        <netcdf
location="http://coast-enviro.er.usgs.gov/models/gom_interop/coastwatch_northeast_lonlat.nc"/>
        <netcdf
location="http://coastwatch.chesapeakebay.noaa.gov/dap/edac/avhrr/data/2008_135_0921_noaa15_ex1_sst.hdf"/>
     </aggregation>
</netcdf>

I can also aggregate the HDF5 images along a virtual time dimension
and then union with the netcdf file that has the lon/lat values, and
it works -- only remaining issue is that the scale_factor is lost for
some reason, which I'm looking into.

Try getting http://coast-enviro.er.usgs.gov/models/share/coastwatch.zip
and running "test_sst", then looking at the two NcML files "sst.ncml"

-Rich

On Fri, May 30, 2008 at 9:20 AM, David Robertson
<robertson@xxxxxxxxxxxxxxxxxx> wrote:
> Hi,
>
> If I want to serve aggregated HDF5 files, do I have to specify the
> coordinate system (grid) with NcML, or is there a way to construct the
> HDF5 file so THREDDS can get the coordSys directly from the HDF5 file? I
> ask because if my only option is NcML I will ask my "data source" to
> create NetCDF files instead since the coverage area is 1222 x 1183
> points and they are not equal spaced.
>
> Thanks,
> Dave
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-- 
Dr. Richard P. Signell (508) 457-2229
USGS, 384 Woods Hole Rd.
Woods Hole, MA 02543-1598

Attachment: coastwatch.zip
Description: Zip archive

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