Re: Suggestion for Coordinate Mapping convention

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: Re: Suggestion for Coordinate Mapping convention
• From: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
• Date: Wed, 21 Oct 1992 13:06:22 -0600

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

In the above message Steve Hankin wrote:

>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";

Because we might wish to generalize this virtual variable mechanism at some
later date, I would argue for the following (slight) variation:

               char velocity(vector_def);          // ** dummy variable **//
                        velocity:long_name = "3-component velocity";
                        velocity:definition = "(u,v,w)";

That is: 1) the use of the attribute `definition' rather than `components';
and 2) the use of a mathematial expression for the value of the `definition'
attribute.

I'm not happy about the `char velocity(vector_def)' expression because it
appears too artificial.  But, without adding, for example, a `virtual'
keyword to the CDL files and supporting the creation of virtual variables
in the netCDF API, this is probably as good as we can do for the moment.

--------
Steve Emmerson   <steve@xxxxxxxxxxxxxxxx>

• References:
  • RE: Suggestion for Coordinate Mapping convention
    • From: HANKIN