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#109: resolve inconsistency of positive and standard_name attributes
----------------------------+-----------------------------------------------
 Reporter:  jonathan        |       Owner:  [email protected]
     Type:  defect          |      Status:  new                          
 Priority:  medium          |   Milestone:                               
Component:  cf-conventions  |     Version:                               
 Keywords:                  |  
----------------------------+-----------------------------------------------
 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:

   Recommendations:

   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.

 Jonathan

-- 
Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/109>
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