Custom Query (125 matches)

Filters
 
Or
 
  
 
Columns

Show under each result:


Results (82 - 84 of 125)

Ticket Resolution Summary Owner Reporter
#103 fixed Corrections to Appendices A and H davidhassell ros
Description

Appendix A:

  • cf_role, featureType, instance_dimension and sample_dimension should all be of type "S" not C or N.
  • It is not obvious that the "Use" should be D for instance_dimension and sample_dimension. The count and index variables are not data variables, but not coord vars either. Suggest putting "-" for them, and add to the key that "-" is for variables with a special purpose.

Appendix H:

  • Section H2: In the examples station_name is an auxiliary coord var and so needs to be identified as one in the coordinates attribute.
  • Section H2: _FillValue for the variables humidity and temp should be -999.9f
  • Example H8: coordinates attribute for pressure, temperature and humidity should be set to "time lon lat z"

I've not looked beyond Section H4 so some of these might apply there as well.

#104 fixed Clarify the interpretation of scalar coordinate variables davidhassell jonathan
Description

David Hassell and I propose the following changes to the CF standard document to clarify the interpretation of scalar coordinate variables. We do not think this is a material change to the convention, which already implies this interpretation, and we believe this interpretation is what was intended when scalar coordinate variables were introduced.

Section 5.7, Scalar coordinate variables.

The convention contains the following sentences:

Under COARDS the method of providing a single valued coordinate was to add a dimension of size one to the variable, and supply the corresponding coordinate variable. The new scalar coordinate variable is a convenience feature which avoids adding size one dimensions to variables. Scalar coordinate variables have the same information content and can be used in the same contexts as a size one coordinate variable.

These sentences are OK as they stand, we think, but it would be better to describe the current situation without emphasising its history, so we would propose to replace them with the following. In addition, we propose to add a bit extra, as shown, to the second sentence below:

The use of scalar coordinate variables is a convenience feature which avoids adding size one dimensions to variables. A scalar coordinate variable has the same information content and can be used in the same contexts as a size one coordinate variable, if numeric, or a size one auxiliary coordinate variable, if a string (Section 6.1).

The next sentence would be unchanged; it mentions how this situation relates to that of the COARDS convention.

At the end of the section, after the example, we propose to append the following sentences:

If a data variable has two or more scalar coordinate variables, they are regarded as though they were all independent coordinate variables with dimensions of size one. If two or more single-valued coordinates are not independent, but have related values (for instance, time and forecast period, or vertical coordinate and model level number, Section 6.2), they should be stored as coordinate or auxiliary coordinate variables of the same size one dimension, not as scalar coordinate variables.

We think the above interpretation and implications are consistent with the convention already, which says in this section that, "Scalar coordinate variables have the same information content and can be used in the same contexts as a size one coordinate variable". However, it would be an improvement to spell it out.

Section 6.1, Labels

Replace the last sentence

If a character variable has only one dimension (the maximum length of the string), it is regarded as a string-valued scalar coordinate variable, analogous to a numeric scalar coordinate variable (see Section 5.7, Scalar Coordinate Variables).

with

If a character variable has only one dimension (the maximum length of the string), it is a string-valued scalar coordinate variable (see Section 5.7, Scalar Coordinate Variables). As such, it has the same information content and can be used in the same contexts as a string-valued auxiliary coordinate variable of a size one dimension. This is a convenience feature which avoids adding the size one dimension to the data variable.

The last part is a repetition of what Section 5.7 says. The reason for the change is that the existing wording is careless in implying that a string could be a coordinate variable; in fact, this is not possible, since string- value coordinates must be auxiliary coordinate variables.

The interpretation of scalar coordinate variables in Section 9 may be different from the above, and this may require further clarification if the above is agreed.

#105 wontfix Scalar Coordinates cf-conventions@… markh
Description

1. Title

Scalar Coordinates

2. Moderator

unknown

3. Requirement

The ability to store scalar coordinates in CF NetCDF data sets.

Scalar Coordinates are a valuable semantic concept, allowing data variables to encode coordinates which do not vary across the domain of the data variable.

Invariance with respect to the data variable's dimensions is the key characteristic of these coordinates and this is all the meaning that should be explicitly defined for such a coordinate. Further characteristics, such as implied degrees of freedom and potential inter-relationships, may be inferred downstream, at the discretion of the data consumer.

The current conventions provides clear specification on vector coordinates, encoded as either Coordinate Variables or Auxiliary Coordinate Variables. Such variables, which may be encoded as not varying with respect to the data variable, can be used wherever it is vital that the inter-relationship and degree of freedom are explicitly encoded. The specification does not make it clear enough what is meant by a scalar coordinate variable.

The current conventions document (1.6) does not make it clear whether the scalar coordinate variable (section 5.7) is:

an encoding detail with explicitly no semantic content, merely storing vector coordinates:

where the characteristics of these vector coordinates must be inferred by context;

a semantic container enabling scalar coordinates to be stored and recognised as scalar coordinates.

This interpretation requires clarification, which this proposal aim to deliver. Explicitly, this proposal will define the scalar coordinate variable as a semantic container for coordinate information.

4. Initial Statement of Technical Proposal

1.2 Terminology

A NetCDF variable which contains coordinate information for a data variable, where the coordinate information does not vary with respect to the data variable's dimensions.

5.7 Scalar Coordinate Variables

A scalar coordinate variable defines a coordinate which applies to an entire data variable equally. The scalar coordinate does not vary with respect to the data variable's dimensions.

The scalar coordinate variable is associated with a data variable via the coordinates attribute. The scalar coordinate variable does not share any dimensions with the data variable.

The variable name of a scalar coordinate variable must not match the name of any dimension in the file.

Bounds may be defined for a scalar coordinate variable in the same way as other coordinates.

A scalar coordinate variable may be interpreted as implying a potential further dimension, of size one, for the data variable. However, scalar coordinate variables do not define explicit independent dimensions.

Note that use of scalar coordinate variables for latitude, longitude, vertical, or time coordinates will inhibit COARDS conforming applications from recognizing them.

6.1 Labels

... {Unchanged, up to the last sentence}

If a character variable referenced by a data variable's coordinates attribute has only one dimension, the maximum length of the string, it is a string-valued scalar coordinate variable (see Section 5.7 Scalar Coordinate Variables).

9.2 Collections, Instances and Elements

... {First two paragraphs unchanged}

If there is only a single feature to be stored in a data variable, the instance dimension may be omitted. In this case the mandatory space-time coordinate variables will not vary with respect to the instance dimension. These space-time coordinates, as defined in table 9.1, may need to be defined as scalar coordinate variables, to maintain the required relationships for the feature types.

5. Benefits

The community benefits from this proposal by gaining clarity over the interpretation of scalar coordinate variables as a simple semantic concept within CF with a clear encoding.

All use cases presented to the mailing list to date are supported by this proposal, including:

  • encoding of size one explicit coordinate variables as scalar coordinate variables to simplify data variable shape;
  • encoding of coordinates where there are multiple possible inter-dependency relationships, such as:
    • multiple related time coordinates;
    • model, experiment, run identifiers for multi-model analyses;
  • encoding of discrete sampling geometries where there is a single feature;
  • encoding of coefficients as coordinates.

The data producer has the opportunity to select a scalar coordinate as the most appropriate way of describing some aspects of their data. The encoding convenience of omitting dimensions of size one is provided for, with a clear recognition that this encoding option slightly limits the richness of expression available with CF vector coordinates.

6. Status Quo

Currently the interpretation of scalar coordinate variables is unclear. It is recognised that a clarification is required. As such the status quo is deemed undesirable (e.g.4, 15)

There is another ticket, #104, proposing an alternative change. These two tickets should not both be approved, they are mutually exclusive.

Note: See TracQuery for help on using queries.