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
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