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Ticket Resolution Summary Owner Reporter
#76 fixed More than one name in Conventions attribute davidhassell Dave.Allured


It is proposed to support the listing of more than one convention name in the Conventions global attribute. As of CF-1.6, only the CF identification by itself is allowed. The option of a list has been in Unidata's recommendations for a long time; see references. There was some community support for this in the recent mailing list discussion.


I would like to present this in two parts. This trac ticket is part 1, which proposes to adopt verbatim, the Unidata language for listing more than one convention name. The original Unidata recommendation allows the list of names to be separated by either spaces or commas.

Part 2, which I plan to file as a separate ticket, would propose more detailed parsing rules and would probably replace the syntax description of part 1. The main objectives of part 2 would be to accommodate both unambiguous machine parsing, and flexibility in allowable characters in convention names.

Why two tickets? I think that part 1 has a better chance of approval. It accomplishes the most important objective of multiple conventions in a workable way. If part 2 succeeds, it can replace part 1, sooner or later.

The mailing list discussion beginning December 2011 should be considered part of the record for this proposal.

Text of proposed changes

Two new paragraphs are to be added at the end of the current section 2.6.1, Identification of Conventions:

It is possible for a netCDF file to adhere to more than one set of conventions, even when there is no inheritance relationship among the conventions. In this case, the value of the Conventions attribute may be a single text string containing a list of the convention names separated by blank space (recommended) or commas (if a convention name contains blanks). This is the Unidata recommended syntax from NetCDF Users Guide, Appendix B.

When CF is listed with other conventions, this asserts the same full compliance with CF requirements and interpretations as if CF was the sole convention. It is the responsibility of the data-writer to ensure that all common metadata is used with consistent meaning between conventions.

In the conformance document, add a new second line under 2.6.1 Identification of Conventions:

  • The Conventions attribute may be a single text string containing a list of convention names separated by blank space or commas, one of which shall be the full CF string as described above.


Current language of section 2.6.1, Identification of Conventions (CF-1.6)

NetCDF Users Guide, Appendix B, Attribute Conventions

List of registered conventions, NetCDF website

Ticket #27, Use namespace tags to include other conventions, 2008
(Previous proposal and discussion of Conventions attribute, not yet adopted)

#48 fixed Minor typo in equivalent_reflectivity_factor definition apamment Greg Rappa

The word reflectivity is spelled incorrectly as "relectivity".

This typo appears in both files: cf-standard-name-table.html and cf-standard-name-table.xml

#33 fixed cell_methods for statistical indices jonathan Heinke
  1. Title

New cell_method 'count over days'

  1. Moderator

Jonathan Gregory

  1. Proposing

New entry for table E.1. Cell Methods:

name='count over days' Units=1 description='the number of occurences of a condition specified in the standard name'

The Units are Integer.

4.Use Cases

For statistic indices we like to add the following new standard_names:



frost_days min<0 degC = fd (IPCC AR4 and AR5)

ice days max<0 degC

frost days where no snow

number_of_days_with_air_temperature_above_threshold examples:

summer days max>25 degC

tropical nights min>20 degC



heavy precipitation >10 mm = r10 (IPCC AR4 and AR5)

very heavy precipitation >20 mm

wet days > 1mm



strong breeze days max > 10,5 m/s

strong gale days max > 20,5 m/s

hurricane days max > 32,5 m/s

To specify the standard_name the CDLs should have the following form:

/* number of days with daily minimum below 0 degC = frost_days = fd (IPCC AR4 and AR5) */ float n1(lat,lon);

n1:standard_name="number_of_days_with_temperature_below_threshold"; n1:coordinates="threshold time"; n1:cell_methods="time: count over days";

float threshold;

threshold:standard_name="air_temperature"; threshold:units="degC"; threshold:cell_methods="time: minimun within days"



Best regards Heinke

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