Re: re Unidata Observation Dataset Conventions

Hi Stu:

Stuart Wier wrote:

I am using your web page
to try to make proper NetCDF point observation files for the IDV.

There is only one sample cdl file, for trajectory data, so I have some questions about making a good point observations cdl file. My sample cdl file is attached.

The web page says "The latitude variable is named by the global attribute latitude_coordinate"
yet the sample cdl file does not have latitude_coordinate.
Is global attribute latitude_coordinate required?

The web page says
"The latitude variable must have an attribute named _CoordinateAxisType with value equal to "Lat".
yet the sample cdl file has no attribute named _CoordinateAxisType.
(Don't the special required names latitude, longitude etc. fill this role?)

There are 4 alternate ways to name the coordinate variables, so you want to choose which 
to use. Naming them explcitly "latitude" etc as you have is the best, IMO, 
because other programs are likely to recognize them.

I assume "record" is a good observation dimension, as in the attached cdl, and that "UNLIMITED" is valid.

record is the default, so its fine

In the sample cdl file the :Conventions attribute has only :Conventions = "CF-1.0" while you have recommended
:Conventions = "CF-1.0, Unidata Observation Dataset v1.0";

At this point, I prefer just "Unidata Observation Dataset v1.0", because the CF 
conventions are not complete for obs data, and as i understand, they will withdraw their 
recomendations until they are more complete.

I will fix my example cdl, thanks for pointing that out.

Please let me know if this cdl file is an ok point observations file.

The Unidata IDV 1.3b1 will accept this file as a data source, but no Fields (variables)
are recognized.

I will look into that, send me a data file with some data in it when you can so 
i can test.

When I have a working point observations cdl file you are welcome to
use it in your webpage.

Thanks very much, sorry about the usual primitive state of the documentation. I 
will make some incremental improvements to it based on your feedback.


netcdf strain_data_synthetic {
        record = UNLIMITED ;
   double time(record);
     time:long_name = "time GMT";
     time:units = "seconds since 1970-01-01 00:00:00";
     time:_CoordinateAxisType = "Time";
   double depth(record);
depth:long_name = "depth of instrument below surface at observing site";
     depth:standard_name = "depth";
     depth:units = "m";
     depth:positive = "down";
     depth:_FillValue = 1.0E-34; // double
     depth:_CoordinateAxisType = "Height";
   double latitude(record);
     latitude:long_name = "latitude";
     latitude:standard_name = "latitude";
     latitude:units = "degrees_north";
     latitude:_FillValue = 1.0E-34; // double
     latitude:_CoordinateAxisType = "Lat";
   double longitude(record);
     longitude:long_name = "longitude";
     longitude:standard_name = "longitude";
     longitude:units = "degrees_east";
     longitude:_FillValue = 1.0E-34; // double
     longitude:_CoordinateAxisType = "Lon";

   float eps2_az(record) ;
eps2_az:long_name = "azimuth of eps2, degrees clockwise from true north" ;
     eps2_az:units = "degrees" ;
   float eps2(record) ;
     eps2:long_name = "earth strain rate; most compressional eigenvalue" ;
     eps2:units = "10-9 per year" ;
   float eps1(record) ;
     eps1:long_name = "earth strain rate; most extenional eigenvalue" ;
     eps1:units = "10-9 per year" ;

// global attributes
        :cdm_datatype = "Point";
        :title = "short description of what is in the dataset";
        :summary = "a paragraph describing the dataset" ;
:keywords = "a comma-separated list of keywords and phrases, earth strain, stain axes" ;
        :Conventions = "CF-1.0, Unidata Observation Dataset v1.0";
        :Metadata_Conventions = "Unidata Dataset Discovery v1.0";
        :creator_name = "M. Faraday" ;
        :creator_url = ""; ;
        :creator_email = "DrElectricity@xxxxxxxxxxxxxxxxx" ;
        :institution = "where produced";
:acknowledgment = "various types of support for the project that produced this data" ; :references = "publications or web references that describe data or its production"; :history = "audit trail for modifications, with dates, version numbers, etc.";
        :comment = "miscellaneous information";
        :geospatial_lat_min = "-90.0" ;
        :geospatial_lat_max = "90.0" ;
        :geospatial_lat_units = "degrees_north" ;
        :geospatial_lat_resolution = "0.01" ;
        :geospatial_lon_min = "-180.0" ;
        :geospatial_lon_max = "180.0" ;
        :geospatial_lon_units = "degrees_east" ;
        :geospatial_lon_resolution = "0.01" ;
        :geospatial_vertical_min = "0" ;
        :geospatial_vertical_max = "0" ;
        :geospatial_vertical_units = "meters" ;
        :geospatial_vertical_resolution = "1." ;
        :geospatial_vertical_positive = "down" ;
        :time_coverage_start = "1999-07-04T22:30" ;
        :time_coverage_end = "2003-05-05T18:50:34Z";
        :time_coverage_resolution = "sec" ;


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