Dear All,
Reading this reminds me of an issue I need to address locally. We have units
'Degrees magnetic' and 'Degrees true' in our data system (many current meters
are calibrated to magnetic and subsequently corrected to true). The local
approach I am trying to take is to move the semantics to the parameter
description (Standard Name 'equivalent'). However, I guess I'm not alone in
needing to provide labels to data in both co-ordinate systems, so agreeing a
policy on how this situation is handled in CF could be helpful.
Cheers, Roy.
________________________________
From: [email protected] [[email protected]] On
Behalf Of Comiskey, Glenn [[email protected]]
Sent: 14 July 2011 15:48
To: [email protected]
Subject: [CF-metadata] Units: degrees - COARDS/CF Convention
Hi,
The use of the variable unit value "degrees" would appear to discount a data
set from being both COARDS and CF compliant, at least according to the CF
conventions document, i.e. v1.5, section 3.1 states "The COARDS convention
prohibits the unit "degrees" altogether" while also stating "this unit is not
forbidden by the CF convention". Is this in fact true?
The COARDS convention does indeed state, when refering to UDUNITS, "names
therein...will be regarded as acceptable unit names for this standard with the
following additions and deletions: "degrees" - deleted". However, it then goes
on to say "The unit "degrees" creates ambiguities when attempting to
differentiate longitude and latitude coordinate variables; files must use
"degrees_east"...and "degrees_north"".
Is it not a case that the COARDS convention is disallowing the use of the
"degrees" value simply for coordinate variables, and subsequently mandating the
use of "degrees_east" and "degrees_north", to remove any potential ambiguity
with regards to the position the data relates, i.e. COARDS requires
"degrees_east" and "degrees_north" for coordinates variables, but allows uses
of "degrees" for a data variable such wind direction (NOTE: I am aware that the
CF standard canonical unit is "degree").
Is there some convention (pun intended :-) to interpretating the COARDS
convention as meaning that "degrees" is prohibited, period?
Kind regards,
Glenn Comiskey
Data System Administrator
Fugro Global Environment & Ocean Sciences
Fugro House, Hithercroft Road
Wallingford, Oxfordshire OX10 9RB, UK
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