Re: [netcdf-java] [netcdfgroup] grid not recognized

• To: Frank Platzek <Frank.Platzek@xxxxxxxxxxx>
• Subject: Re: [netcdf-java] [netcdfgroup] grid not recognized
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Tue, 27 Jan 2009 08:35:44 -0700

Hi Frank:

The right way to do this is to follow the CF Conventions at

  http://cf-pcmdi.llnl.gov/documents/cf-conventions/

A minimum thing to do is to add a global attribute:

   :Conventions = "CF-1.0";

The problem is that ncwms/cdm is not recognizing the sigma coordinate as the 
vertical coordinate.
The right thing to do is to change it to one of the recognized CF vertical 
coordinates in appendix
D, adding the correct metadata to allow transformation to height or pressure. 
As a quick fix you can
add this attribute to the sigma variable:

  sigma:axis = "Z";

These 2 changes will allow viewing in toolsUI and IDV.

You also dont have projection information, so the x and y coordinates are not 
useable. The 2D
lat/lon will be used instead, though there is some loss of funcionality and 
efficiency when
computing subsets. In fact, im not sure if ncwms will work with only 2D lat/lon 
coordinates, you
should post that question to that group (ncwms-users@xxxxxxxxxxxxxxxxxxxxx). 
The right thing is to
add projection information using appendix F.

If these are important files you want to make as readable as possible by other 
tools, i would
strongly suggest taking the time to add the vertical transform and projection 
info, and making sure
the file is CF compliant. Two useful tools for that are:

  http://cf-pcmdi.llnl.gov/conformance/compliance-checker/

  http://motherlode.ucar.edu:8080/thredds/cdmValidate.html

Regards,
John


Frank Platzek wrote:
> Hi all,
> 
> I created a netcdf file which I want to use with ncwms. The file is not
> recognized by ncwms. I also tried toolsui 2 & 4 and idv. But non of the
> tools I tried seem to recognize my file as a gridded dataset.  Do you
> have any suggestions on how to improve it? You can find the header below.
> 
> Kind regards,
> 
> Frank
> 
> 
> 
> netcdf p04 {
> dimensions:
>     x = 50 ;
>     y = 50 ;
>     sigma = 5 ;
>     time = UNLIMITED ; // (6 currently)
> variables:
>     float x(x) ;
>         x:units = "m" ;
>     float y(y) ;
>         y:units = "m" ;
>     float sigma(sigma) ;
>     float time(time) ;
>         time:units = "seconds since 1990-08-05 00:00:00" ;
>     double lon(y, x) ;
>         lon:units = "degrees_east" ;
>         lon:standard_name = "longitude" ;
>     double lat(y, x) ;
>         lat:units = "degrees_north" ;
>         lat:standard_name = "latitude" ;
>     float v1(time, sigma, y, x) ;
>         v1:long_name = "Ekofisk" ;
>         v1:_FillValue = 999.999f ;
>         v1:coordinates = "lon lat" ;
>         v1:units = "kg/m2" ;
>     float v8(time, sigma, y, x) ;
>         v8:long_name = "LocalDepth" ;
>         v8:_FillValue = 999.999f ;
>         v8:coordinates = "lon lat" ;
>         v8:units = "m" ;
> }
> 
> 
> 
> 
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