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Re: angular variable attributes?

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  • Subject: Re: angular variable attributes?
  • Date: Wed, 21 Aug 2002 11:20:14 -0600
Hi Chris,

>       Is there a standard for specifying angular variables (e.g. Longitude or 
> Heading that "wrap around")?
> 
> I was going to add something like:
> 
>       :angular_range = 0.0, 360.0;

There are several conventions for longitude, such as the CF
convention and the COARDS convention:

  http://www.cgd.ucar.edu/cms/eaton/netcdf/CF-working-nochange.html
  http://ferret.wrc.noaa.gov/noaa_coop/coop_cdf_profile.html

The latter says:

  Longitudes may be represented modulo 360. Thus, for example, -180,
  180, and 540 are all valid representations of the International
  Dateline and 0 and 360 are both valid representations of the Prime
  Meridian. Note, however, that the sequence of numerical longitude
  values stored in the netCDF file must be monotonic in a non-modulo
  sense.

but doesn't say how this can be specified by an attribute.  I know
there are other uses for modulo or wrap-around domains, such as months
of the year for climate data or hour of the day for observations, but
I don't know that anyone has proposed a general attribute to represent
this.

There was some discussion of a suggestion by Peter Cornillon in the
DODS group to provide explicit support for expressing the periodic
nature of some variables, but so far DODS has not adopted it:

  
http://www.unidata.ucar.edu/projects/coohl/mhonarc/MailArchives/dods-tech/msg00839.html

--Russ