On 7/18/2011 3:42 AM, Comiskey, Glenn wrote:
> Hi,
> The COARDS covention mandates the use of the "positive" attribute for
> a vertical axis that is not a unit of pressure, i.e. if using metres
> to denote altitude. It further qualifies use of the "positive"
> attribute as a means of discovering vertical coordinate variables,
> i.e. the convention states "A vertical coordinate variable will be
> identifiable by: units of pressure; or the presence of the positive
> attribute..." Does this, therefore, restrict use of the "positive"
> attribute to vertical coordinate variables only? NOTE: CF convention
> (v1.5, Appendix A: Attributes, page 50) reports use of the "positive"
> attribute as relating to coordinate data only.
> I ask as I have a number of datasets in which the vertical coordinate
> variable is present, named "altitude" albeit it represents sea level
> with a value of 0 (zero), unit value of metres and has a
> declared "positive" attribute of "up", but also contains tidal data
> reporting the height of the water column above a pressure gauge and an
> attribute is wanted to be added to denote that increasing values
> represent a greater depth of water, i.e. "positive" is down. Would use
> of the "positive" attribute for data variables interfere with the
> discovery of vertical coordinates as defined by COARDS?
Hi Glenn:
The CDM library wont have trouble with that attribute on data variables,
but im not sure about other libraries.
Really theres no good reason not to unambiguously label coordinates,
rather than relying on units or attributes like "positive". Why risk
having a library misunderstand? At this point, the best existing
candidate for CF would be the "axis" attribute. However, people are
usually worried about legacy applications, and theres probably not a
definitive solution for those.
John
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20110719/71d4f0a7/attachment-0001.html>
Received on Tue Jul 19 2011 - 19:13:45 BST
