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#107: CF Data Model 1.7
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Reporter: markh | Owner: cf-conventions@…
Type: task | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords:
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Comment (by biard):
Replying to [comment:53 markh]:
> Replying to [comment:52 biard]:
>
> ...
>
> Are you content that this interpretation provides your ''superior
approach'': that ''coordinates directly reference their coordinate
systems''?
>
> mark
Mark,
Sorry I didn't get back to this sooner. I agree that the suggested new
syntax for the contents of the grid_mapping attribute addresses the
problem of how to have different CRSs for different coordinate variables,
but I don't think it's true that the current highly indirect way of
connecting coordinate variables to coordinate systems is semantically
equivalent to having a coordinate variable directly reference its CRS.
It's easy to see that this is true when you ask the question, "Can I
associate multiple CRSs with a single coordinate variable using this
scheme?"
Let's say I have two data variables that both use the same coordinate
variable, and thus two statements of the association between the
coordinate variable and a CRS. With the current solution, the answer is
"Yes". We must rely on the developer / CF checker to avoid this condition.
If a coordinate variable directly references its CRS, the answer is "No".
The two solutions are not equivalent.
If you are trying to be rigorous in your description of the data model,
then I don't think you can say that a coordinate variable references a
CRS. You can say:
A coordinate must be associated with not more than one CRS, and all
data variables referencing a given coordinate must declare the same
association.
Or something along those lines.
Grace and peace,
Jim
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Ticket URL: <http://kitt.llnl.gov/trac/ticket/107#comment:57>
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