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[CF-metadata] the need to store lat/lon coordinates in a CF metadata compliant netCDF file

From: John Caron <caron>
Date: Thu, 07 Jul 2011 17:54:34 -0600

On 6/30/2011 1:26 PM, Randy Horne wrote:
> Paragraph 5.6 Coordinate Reference Systems, Grid
> Mappings, and Projections, first sentence:
>
> When the coordinate variables for a horizontal grid are not longitude and latitude, it is required that the true latitude and longitude coordinates be supplied via the coordinates attribute.
>
> Are there any exceptions to this "rule" ?
>
> The reason for asking is based on a scenario where the coordinate system and constituent locations for the data points associated with the gridded data set can be determined solely based on the grid mapping.
>
> The reason for wanting to do this is to minimize the size of the netCDF file, and the hardware resources required to process, store, and distribute the file.
>
>
Hi Randy:

There has been no formal exception granted from this rule. The java
netcdf library does not require lat/lon as long as a valid grid mapping
is supplied. In that case, the lat/lon arrays are 2D, and can be a
significant size. When writing "CF compliant" netcdf files (eg from
netcdf subset service), the user is allowed to decide to include lat/lon
or not. Technically if not included, the files are not fully CF compliant.

CF has mostly thought about how to make archival model data as
self-contained as possible, thus the insistence on lat/lon arrays. I
think there are other valid uses of netcdf-CF files, eg as an exchange
format, and that the lat/lon arrays should be optional. There is
currently no mechanism, eg a "profile" of CF to allow that.

John
Received on Thu Jul 07 2011 - 17:54:34 BST

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