RE: Suggestion for Coordinate Mapping convention

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: RE: Suggestion for Coordinate Mapping convention
• From: HANKIN@xxxxxxxxxxxx
• Date: Wed, 21 Oct 1992 10:53:33 -0700 (PDT)

Hello Rich, Tim, et. al.,

I agree, netCDF **needs** to provide a standardized mechanism for storing 
vector 
data (multiple compionents) and "irregular" grids (in the AVS sense you 
described).  I will incorporate your ideas (in bullet form) into the "straw 
man" 
conventions.

I would like to propose a variation on the theme you set out, Rich.

Your proposed "Convention 1" to accomodate vector components is:

         dimensions:
               lat=20,lon=20,components=3;
         variables:
               float velocity(lat,lon,components);


The difficulty with this is that it limits the richness of the file in 
describing the individual components.  For example, the Z velocity component 
("W" in U,V,W) would often be determined by an entirely different means than U 
and V.  Since W is never broken out as a separate variable this becomes 
difficult to document.

I suggest the use of "dummy" variables for the purpose of binding together 
components:

         dimensions:
               lat=20,lon=20,depth=5,vector_def=1;
         variables:
                float u(lat,lon,depth);
                        u:long_name = "zonal speed";
                float v(lat,lon,depth);
                        v:long_name = "meridional speed";
                float w(lat,lon,depth);
                        w:long_name = "upwelling computed by divergence ...";
               char velocity(vector_def);          // ** dummy variable **//
                        velocity:long_name = "3-component velocity";
                        velocity:components = "u v w";

Besides the advantage of righ meta-data storage for the components this has 
another major selling point: if the dummy variable is ignored this is a 
completely conventional netCDF file.  This means that generic, current netcdf 
files could be converted to this form simply by adding dummy variables and 
their 
attributes.

I will include your "Convention 1" and this variation as Proposals in "A 
Strawman Profile for Oceanographic NetCDF Files".  I will also include  
your (important) "Convention 2".  It directly addresses the need for the 
storage 
of "irregular" data types like ship-track observations.

                |  NOAA/PMEL               |  ph. (206) 526-6080
Steve Hankin    |  7600 Sand Point Way NE  |  FAX (206) 526-6744
                |  Seattle, WA 98115-0070  |  hankin@xxxxxxxxxxxx

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  • Re: Suggestion for Coordinate Mapping convention
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