Fwd: Re: GMU WCS Server supports netCDF output

• To: galeon@xxxxxxxxxxxxxxxx
• Subject: Fwd: Re: GMU WCS Server supports netCDF output
• From: yliu5@xxxxxxx
• Date: Thu, 25 Aug 2005 16:10:33 -0400

:)

Hi Frank,

I believe the file is correct. Please refer to CF conventions document at

http://www.cgd.ucar.edu/cms/eaton/cf-metadata/CF-1.0.html

Chapter 5.6 and Appendix F.

Actually the data is in UTM projection, but I can't find how to specify UTM in 
netCDF. So I used Transverse Mercator instead. Is there any other way to 
specify projections?

There are two variables called xdim and ydim. From them you can get the 
x-coordinate and y-coordinate of every pixel. Therefore we can get anything we 
want such as the offset, origin, etc. And also there are lat/lon variables 
storing the lat/lon of every pixel. That makes the netCDF file much larger than 
the original HDF-EOS file. If you have any better idea to avoid those 
unnecessary variables, please let me know. Thanks.

Regards,
Yang Liu
LAITS,GMU

----- Original Message -----
From: Frank Warmerdam <fwarmerdam@xxxxxxxxx>
Date: Thursday, August 25, 2005 12:58 pm
Subject: Re: GMU WCS Server supports netCDF output

Yang Liu,

The ncdump of this result looks like:

netcdf wcs100 {
dimensions:
       xdim = 813 ;
       ydim = 711 ;
variables:
       double xdim(xdim) ;
               xdim:standard_name = "projection_x_coordinate" ;
               xdim:units = "m" ;
       double ydim(ydim) ;
               ydim:standard_name = "projection_y_coordinate" ;
               ydim:units = "m" ;
       int projection ;

projection:grid_mapping_name = "transverse_mercator" ; projection:scale_factor_at_central_meridian = 0.9996 ;

               projection:longitude_of_central_meridian = 99 ;
               projection:latitude_of_projection_origin = 0 ;
               projection:false_easting = 500000 ;
               projection:false_northing = 0 ;
       double lon(ydim, xdim) ;
               lon:standard_name = "longitude" ;
               lon:units = "degrees_east" ;
               lon:long_name = "longitude" ;
       double lat(ydim, xdim) ;
               lat:standard_name = "latitude" ;
               lat:units = "degrees_north" ;
               lat:long_name = "latitude" ;
       byte L71131056_05620041229_B10(ydim, xdim) ;
               L71131056_05620041229_B10:long_name
"L71131056_05620041229_B10" ;
               L71131056_05620041229_B10:coordinates = "lat lon" ;

L71131056_05620041229_B10:grid_mapping = "projection" ;

// global attributes:
               :institution = "LAITS, GMU" ;
               :Conventions = "CF-1.0" ;
...

Is the set of projection parameters standard? Currently the GDAL NetCDFdriver does not seem to support your coordinate system conventions. In fact, I find it odd that you list projection parameters but you don'tgive any bounds or other information about the image in that projection.I think we need a way of encoding the projected origin and offset

vector information in the netcdf result.  You obviously have it for

generating the coverage description.

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