Custom Query (124 matches)

Whilst correcting some bugs in the CF checker I came across some errors/omissions in the CF Conventions document and Conformance Document. I propose the following changes.

2.5.1 Missing Data
The table in Appendix A incorrectly states that missing_value and _FillValue are Numeric attributes. This is inconsistent with CF 2.5.1, which says, "The scalar attribute with the name _FillValue and of the same type as its variable is recognized by the netCDF library as the value used to pre-fill disk space allocated to the variable."

The correction required is:

In Appendix A change the type from N to D for missing_value and _FillValue in the table.

3.3 Standard Name Modifiers
The requirements and recommendations for standard name modifiers are missing from the Conformance document.

Change Section 3.3 to

3.3 Standard Name
Requirements:
 * The standard_name attribute takes a string value comprised of a standard
   name optionally followed by one or more blanks and a standard name
   modifier.
 * The legal values for the standard name are contained in the standard name
   table. 
 * The legal values for the standard name modifier are contained in Appendix C,
   Standard Name Modifiers.

5.6 Grid Mappings and Projections
The requirements and recommendations for grid mappings are missing from the Conformance document.

Add a section

5.6 Grid Mappings and Projections

Requirements:
 * The type of the grid_mapping attribute is a string whose value is a single
   variable name.
 * The specified variable name (known as a grid mapping variable) must exist
   in the file.
 * The grid mapping variable must have the grid_mapping_name attribute. The 
   legal values for the grid_mapping_name attribute are contained in
   Appendix F.
 
Recommendations:
 * The grid mapping variable should have 0 dimensions.

Rosalyn

The Conventions document, version 1.1 at ​http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.1/cf-conventions.html has an error in an entry in the right-hand sub-table of Table 3.1, in section "3.1 Units":

The entry:

1e-2 deci c

should read:

1e-2 centi c

1. Title

Bit field enhancement to CF Flags definition

2. Moderator

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3. Requirement

CF ought to provide a flag expression for multiple conditions, typically Boolean (binary), that describes one or more status conditions associated with a data variable.

4. Initial Statement of Technical Proposal

A new CF flag attribute, named "flag_masks", would enhance the current CF flags capabilities to describe multiple, independent status conditions using bit fields to define unique conditions or status codes.

5. Benefits

Bit field flag attributes are best suited for describing data variables possessing a number of status conditions that typically occur independently of each other.

Bit field attributes would simplify the description of status flags that don't conveniently map to a unique set of mutually exclusive status codes, currently defined with flag_values attributes.

For example, when describing a precipitation measurement within a particular geo-spatial grid, a bit field flag value may be defined to contain four possible binary status conditions, occupying the four least significant bits, whose values would be defined as follows: 1 to indicate no sensor coverage at the grid location, 2 to indicate observation impairment at that grid location, 4 to indicate mixed-phase precipitation at the grid location, 8 to indicate snow precipitation at the grid location.

6. Status Quo

Current flag values could be defined for every OR'ed combination of bit settings that define all possible status conditions, but the result would be inefficient compared to simple bit field definitions.