[thredds] Netcdf Subset Service Questions

• To: thredds community <thredds@xxxxxxxxxxxxxxxx>
• Subject: [thredds] Netcdf Subset Service Questions
• From: Roy Mendelssohn <Roy.Mendelssohn@xxxxxxxx>
• Date: Fri, 7 Oct 2011 11:40:34 -0700

Hi All:

We have some questions (or possible suggestions) about the NetCDF subset 
service.

1.  Following the CF conventions, we have lat, lon, and time variables with 
attributes as follows:

        double time(time) ;
                time:long_name = "reference time" ;
                time:units = "days since 1998-01-01 " ;
                time:bounds = "time_bnds" ;
                time:_CoordinateAxisType = "Time" ;
        float lat(lat) ;
                lat:long_name = "latitude" ;
                lat:units = "degrees_north" ;
                lat:bounds = "lat_bnds" ;
                lat:_CoordinateAxisType = "Lat" ;
                lat:standard_name = "latitude" ;
        float lon(lon) ;
                lon:long_name = "longitude" ;
                lon:units = "degrees_east" ;
                lon:bounds = "lon_bnds" ;
                lon:_CoordinateAxisType = "Lon" ;
                lon:standard_name = "longitude" ;

Many CF complaint software use the "bounds" information in displaying the data. 
 When the data are subsetted using the subset service, the attributes are 
carried along, but the variables themselves are not.  This then causes display 
programs to throw errors. I would suggest that like the coordinate system 
itself, if the bounds exist they should be subsetted and brought along with the 
file.

2.  We have variables with the following in the original netcdf file:

      float SSTTrimMean(time, lat, lon) ;
              SSTTrimMean:long_name = "Trimmed 1-degree SST Monthly Mean" ;
              SSTTrimMean:units = "degC" ;
              SSTTrimMean:_FillValue = -9999.f ;

When the data are subsetted the returned netcdf file has the same attributes 
but for the missing value now has "NaNf", which again causes a lot of heartburn 
for some display programs.

Thanks,

-Roy


**********************
"The contents of this message do not reflect any position of the U.S. 
Government or NOAA."
**********************
Roy Mendelssohn
Supervisory Operations Research Analyst
NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
1352 Lighthouse Avenue
Pacific Grove, CA 93950-2097

e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
voice: (831)-648-9029
fax: (831)-648-8440
www: http://www.pfeg.noaa.gov/

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