Changes between Initial Version and Version 9 of Ticket #142


Ignore:
Timestamp:
09/24/15 01:28:31 (4 years ago)
Author:
markh
Comment:

It looks from the comments like we are in agreement about the use of axis=E to define that a coordinate is an ensemble coordinate. It also looks like there are good reasons not to rely on a standard name.

I am updating the summary to reflect this.

There is still discussion about how to capture associated metadata, further consideration is needed on this aspect.

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  • Ticket #142 – Description

    initial v9  
    1111    The description of the dimension of a data variable which describes an ensemble of forecasts may involve a number of elements of metadata.
    1212
    13     Such a coordinate is characterised by the `standard_name` `realization`.
     13    Coordinate variables and auxiliary coordinates describing an ensemble need to be able to be labelled as such.
    1414
    1515    It is useful to encapsulate information about the nature of the ensemble with the coordinate.  Current use cases for metadata standardisation are: the original size of the ensemble; the single-model or multi-model nature of the ensemble, the presence of an explicit control forecast as realization=0.
     
    1919    ==== 4.6 Ensemble Coordinate ====
    2020
    21     Variables representing an ensemble or collection of realizations must have a standard_name of `realization` and a units of '1'.  These variables are discrete, as described in section 4.5.  They do not represent continuous quantities.
    22 
    23     Optionally the ensemble coordinate may have an attribute `axis` with a value `E`.
     21    Variables representing an ensemble or collection of realizations shall have an attribute `axis` with a value `E`.  These variables are discrete, as described in section 4.5.  They do not represent continuous quantities.
    2422
    2523    Ensemble variables have a number of optional standardised attributes available for use.  Further bespoke attributes to describe the ensemble in project specific ways are allowed.
     
    4341    ==== 4.6.3 Ensemble Control Member ====
    4442
    45     An ensemble coordinate may include an attribute named `ensemble_control_member_0` representing the interpretation of the realization value of 0. This is a boolean field and may only contain the values `true` or `false`.
     43    An ensemble coordinate may include an attribute named `ensemble_control_member`.
    4644
    47     This value provides a definition that one member of the ensemble is the control member.  This control member shall have the identifying value `0` within the realization dimension.
     45    This value provides a definition that one member of the ensemble is the control member and identifies this member.  This control member shall have the identified value within the ensemble coordinate's data.
    4846
    49     The absence of this attribute shall not be interpreted as a positive or negative statement.  No inference on the interpretation of realization zero within the ensemble shall be inferred from the absence of this attribute.
     47    The absence of this attribute shall not be interpreted as a positive or negative statement.  No inference on the possible presence of a control member shall be inferred from the absence of this attribute.
    5048
    5149