Martin,
We just had some discussion about the proper use of the axis attribute,
but this seems to me like it might be a flaw in the checker. As a scalar
coordinate, height can only be associated with the tas variable via the
coordinates attribute (per section 5.7), but I don't think that makes it
an auxiliary coordinate, does it?
What do other people think? Chime in!
Grace and peace,
Jim
On 5/23/17 10:50 AM, [email protected] wrote:
Hello All,
I'd just like to check one aspect of the conformanc document, which came to our
attention when somebody ran the CF checker on some CMIP5. If you check using
the convention version declared in the file, 1.4, it will raise an error if
there is a scalar coordinate variable with the axis attribute set, e.g.
float tas(time,lat,lon);
......
tas:coordinates = "height" ;
float height ;
....
height: axis = "Z";
In this case "height" variable is, following the logic of section 1.2 of the convention,
classed as an auxillary coordinate because it is not of the form "height (height) ; ".
The error message appears to relate to a line in the conformance document saying that
"The axis attribute is not allowed for auxiliary coordinate variables." If the
checker is asked to use a later version of the convention, the error message goes away,
but the requirement is still there in the conformance document.
It looks to me as though it should be removed from the conformance document. The
convention document says, in section 4. that "The methods of identifying coordinate
types described in this section apply both to coordinate variables", referring to
the use of the axis attribute, which appears to directly contradict the line of the
conformance document cited above. But is there another part of the convention that
requires some restriction on the use of the axis attribute?
This construction is widely used in CMIP data, so we should get this point
cleared up.
regards,
Martin
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