resolve inconsistency of positive and standard_name attributes
|Reported by:||jonathan||Owned by:||davidhassell|
John Graybeal raised the question of what happens if the positive and standard_name attributes of a vertical coordinate variable are inconsistent according to the definition of the latter e.g. if positive="up" and standard_name="depth", which is defined as vertical distance below the surface, implying that positive is down. Steve Hankin and I discussed this on the CF email list and further by email and phone. We would like to propose the following clarification, which should answer the question without materially changing the convention or invalidating existing data.
Append the following to the last paragraph (beginning "Optionally") of introductory part of Section 4.3 (before Section 4.3.1):
If both positive and standard_name are provided, it is recommended that they should be consistent. For instance, if a depth of 1000 metres is represented by -1000 and positive is up, it would be inconsistent to give the standard_name as depth, whose definition (vertical distance below the surface) implies positive down. If an application detects such an inconsistency, the user should be warned, and the positive attribute should be used to determine the sign convention.
Insert the following into Section 4.3 of the conformance document:
The positive attribute should be consistent with the sign convention implied by the definition of the standard_name, if both are provided.
There is no general way to check consistency at present.