#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):
Proposed first paragraph of section 7.1. Cell Boundaries (original
additions marked by ''TEXT'', deletions by ~~TEXT~~, new additions in ''
'''TEXT''' ''):
To represent cells we add the attribute bounds to the appropriate
coordinate variable(s). The value of bounds is the name of the variable
that contains the vertices of the cell boundaries. We refer to this type
of variable as a "boundary variable". A boundary variable will have one
more dimension than its associated coordinate or auxiliary coordinate
variable. The additional dimension should be the most rapidly varying one,
and its size is the maximum number of cell vertices. Since a boundary
variable is considered to be part of a coordinate variable's metadata, it
is not necessary to provide it with attributes (such as `long_name` and
`units`)~~.~~ ''and providing no attributes is always acceptable. Boundary
variable attributes which determine the coordinate type (`units`,
`standard_name`, `axis` and `positive`) or those which affect the
interpretation of the array values (`units`, `calendar`, `leap_month`,
`leap_year` and `month_lengths`) must always agree exactly with the same
attributes of its associated coordinate or auxiliary coordinate variable.
To avoid duplication, however, it is recommended that the attributes
`units`, `standard_name`, `axis`, `positive`, `calendar`, `leap_month`,
`leap_year` and `month_lengths` are not provided to a boundary variable.
'''If the associated variable is a parametric coordinate variable with a
`formula_terms` attribute (ref section 4.3.2) then two cases are
possible'''
'' '''1) if the boundary variable also has a `formula_terms`
attribute then its terms must be the same as those for the parametric
coordinate variable, but with different variables named as term values and
using, wherever possible, the boundary variables of variables named by
parametric coordinate variable's `formula_terms`''' ''
'' '''2) if the boundary variable does not have a `formula_terms`
attribute then it is assumed that the `formula_terms` of the parametric
coordinate variable applies, substituting a named variable with its
boundary variable, wherever possible ''' ''
We'll also need some extra changes to the conformance document ...
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Ticket URL: <https://cf-trac.llnl.gov/trac/ticket/140#comment:4>
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