Re: [netcdfgroup] 2D coordinate variables

• To: "Choonghwan Lee" <cholee@xxxxxxxxxxxx>
• Subject: Re: [netcdfgroup] 2D coordinate variables
• From: "Tom Whittaker" <whittaker@xxxxxxxx>
• Date: Thu, 3 Apr 2008 18:46:40 -0500

If I am not mistaken, you need to define your variable XDim and YDim
as the "coordinate variables", such that the ncdump (or equivalent)
shows:

XDim(XDim);
YDim(YDim);

See section 5.2 of the CF 1 conventions in the document you referenced.

Hope that helps.

tom
On Thu, Apr 3, 2008 at 4:59 PM, Choonghwan Lee <cholee@xxxxxxxxxxxx> wrote:
> Hello,
>
>  While converting HDF-EOS2 files to files that can be read by netCDF4, I got
>  a question regarding coordinate variables. There is a variable that has two
>  coordinate variables: XDim and YDim. I found the following webpage defines
>  what coordinate variable is, but it doesn't mention my case.
>
>  https://www.unidata.ucar.edu/software/netcdf/guidec/guidec-7.html#HEADING7-6
>  7
>
>  The problem is that longitude and latitude cannot be represented as 1d
>  array. To handle this, I referred to CF convention which can be found from
>
>  http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.1/cf-conventions.html#id
>  2617539
>
>  According to the above convention, I generated a file like the following:
>
>   group: Data Fields {
>     dimensions:
>         XDim = 2400 ;
>         YDim = 2400 ;
>     variables:
>         ubyte Snow_Cover_Daily_Tile(YDim, XDim) ;
>            Snow_Cover_Daily_Tile:coordinates = "lon lat" ;
>         double lon(YDim, XDim) ;
>         double lat(YDim, XDim) ;
>
>  It seems this file is a legal netcdf4 file in that ncdump in the latest
>  netCDF4 snapshot does not reject this file. However, I'm wondering if netcdf
>  library recognizes "coordinates" attribute and relates "lon" and "lat" as
>  coordinate variables. If netcdf library does not recognize them, is there
>  any standardized way to inject two-dimensional coordinate variables? I read
>  one draft written in 1997, but I have no idea if this draft was published.
>
>
>  Thanks,
>  Choonghwan Lee
>
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>



-- 
Tom Whittaker
University of Wisconsin-Madison
Space Science & Engineering Center (SSEC)
Cooperative Institute for Meteorological Satellite Studies (CIMSS)
1225 W. Dayton Street
Madison, WI 53706 USA
ph: +1 608 262 2759

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