The CF Specification (
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/ch04s02.html) states:
'Optionally, the longitude type may be indicated additionally by providing the standard_name attribute with the value longitude, and/or the axis attribute with the value X.'
Which suggests that x and longitude are pretty closely bound concepts in CF. It feels to me like longitude is an x-direction, by this text, while other x-directions may also be defined. This seems to support a perspective which states that:
'where longitude is a coordinate variable, the standard_name eastward_*** is an alias for x_***. x_*** defines a vector quantity in the data variable's x direction.'
mark
-----Original Message-----
From: cf-metadata-bounces at cgd.ucar.edu on behalf of Jonathan Gregory
Sent: Sat 21/04/2012 19:08
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] identification of vector components
Dear Jon
I am sure that the phrase "true longitude" in the standard name definition
simply means "longitude", not "x-direction". If there were a need for standard
names which had to distinguish different sort of longitude, that's another
matter, which hasn't been raised before, presumably because "longitude" is
usually accurate enough, certainly for GCMs and for many observational purposes
as well. However it would be possible to have alternative more precise terms.
Best wishes
Jonathan
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Received on Tue Apr 24 2012 - 04:20:48 BST
