#108: Defining a domain for a cell_method
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Reporter: markh | Owner: cf-conventions@…
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords:
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Changes (by cofino):
* cc: antonio.cofino@… (added)
Old description:
> == 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. In this
> case, each 'varname' listed is the name of an ancillary variable,
> explicitly 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.
New description:
== 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. In this
case, each 'varname' listed is the name of an ancillary variable,
explicitly 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.
[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.
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Ticket URL: <http://cf-trac.llnl.gov/trac/ticket/108#comment:11>
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