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#108: Defining a domain for a cell_method
----------------------------+-----------------------------------------------
Reporter: markh | Owner: cf-conventi...@lists.llnl.gov
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Keywords: |
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== 1. Title ==
Defining the domain of operation as part of a cell_method definition.
== 2. Moderator ==
see comments
== 3. Requirement ==
The information contained within a data variable's coordinate may have
value in defining a cell_method for a result data variable calculated from
the initial data variable.
== 4. Initial Statement of Technical Proposal ==
[http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/ch07s03.html
#recording-spacing-original-data 7.3.2 conventions reference]
'''7.3.2. Recording the spacing of the original data and other
information'''
To indicate more precisely how the cell method was applied, extra
information may be included in parentheses () after the identification of
the method. This information includes standardized and non-standardized
parts. ~~Currently the only standardized information is~~ __The interval
spacing keyword is used__ to provide the typical interval between the
original data values to which the method was applied, in the situation
where the present data values are statistically representative of original
data values which had a finer spacing. The syntax is (interval: value
unit), where value is a numerical value and unit is a string that can be
recognized by UNIDATA's Udunits package [UDUNITS]. The unit will usually
be dimensionally equivalent to the unit of the corresponding dimension,
but this is not required (which allows, for example, the interval for a
standard deviation calculated from points evenly spaced in distance along
a parallel to be reported in units of length even if the zonal coordinate
of the cells is given in degrees). Recording the original interval is
particularly important for standard deviations. For example, the standard
deviation of daily values could be indicated by cell_methods="time:
standard_deviation (interval: 1 day)" and of annual values by
cell_methods="time: standard_deviation (interval: 1 year)".
If the cell method applies to a combination of axes, they may have a
common original interval e.g. cell_methods="lat: lon: standard_deviation
(interval: 10 km)". Alternatively, they may have separate intervals, which
are matched to the names of axes by position e.g. cell_methods="lat: lon:
standard_deviation (interval: 0.1 degree_N interval: 0.2 degree_E)", in
which 0.1 degree applies to latitude and 0.2 degree to longitude.
__To explicitly define the domain over which the statistic was
calculated, the syntax (domain: varname varname) may be used. Each
'varname' is the name of an ancillary variable, referenced by the data
variable. Each of the ancillary variables referenced contributes to the
definition of the domain over which the cell_method operation was
conducted.__
== 5. Benefits ==
The community will benefit by having enhanced capabilities for
defining cell_methods for data variables calculated across complex
domains.
[https://cf-pcmdi.llnl.gov/trac/wiki/aggregateExampleMH https://cf-
pcmdi.llnl.gov/trac/wiki/aggregateExampleMH] presents a use case for this
capability.
== 6. Status Quo ==
The capability to define complex domains for cell_methods will not be
standardised.
--
Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/108>
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