#140: Clarifying the role of attributes on boundary variables.
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Reporter: davidhassell | Owner: cf-conventions@…
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords: boundary variable, attribute
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Comment (by davidhassell):
Hello Jonathan, Karl,
I too prefer the "explicit" method, but am quite keen on keeping the
"implicit" method to preserve backwards compatibility. To date, both
methods have been allowed (by virtue of neither being disallowed), so to
preclude the "implicit" method now would cause problems.
I would be more than happy to say that the "explicit" method is strongly
recommended.
Note that the implicit method requires that formula_terms variables with
bounds are auxiliary coordinate variables - otherwise their `bounds`
attributes are not standardised.
Given all that, how about this text, which updates Jonathan's:
If a parametric coordinate variable with a `formula_terms` attribute
(ref section 4.3.2) also has a bounds attribute, it is strongly
recommended that its boundary variable has a `formula_terms`
attribute too. Because the same `standard_name` must describe both
variables, the formula must have the same terms (as specified in
Appendix D), but a different variable must be named by the two
`formula_terms` attributes for any term which depends on the vertical
dimension, because the boundary variables have one more dimension. The
boundary variables for these formula terms may also be identified by
`bounds` attributes of the formula terms variables that are auxiliary
coordinate variables. In that case, the `formula_terms` of the boundary
variable and the bounds of the formula terms variables must be
consistent. If the `formula_terms` attribute is omitted from the
boundary variable then it is assumed that the `formula_terms` attribute
from the parametric coordinate variable applies to the boundary
variable, but for any term which depends on the vertical dimension,
the named variable is replaced with its boundary variable. Therefore,
such a named variable must be an auxiliary coordinate variable with an
associated boundary variable.
All the best,
David
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Ticket URL: <https://cf-trac.llnl.gov/trac/ticket/140#comment:12>
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