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[UDUNITS #PIK-524714]: xlink dictionary references for GCM model output re udunits2 and ISO19115


Sounds like you've got a lot of work on your hands.

The UDUNITS package was designed to parse string unit specifications as 
described by the NIST (see <https://physics.nist.gov/sp811>). It can handle a 
few other styles as well (e.g., a period instead of a half-high dot).

Although we developed the UDUNITS package, we're not familiar with the other 
references you mentioned -- so our help in those areas is limited.

The CF-conventions group has an active mailing-list, if that might help.

Feel free to contact us if you have any issues with the UDUNITS package.

> I seek some input as how to best handle unit references to satisfy
> both UCAR related (e.g. CF-conventions, THREDDS) and ISO19115 conventions.
> Caveat:
> I have until Nov 2017 no experience with the world of Metadata/StyleSheets/
> Transforms/ISO19115/vocabularies.
> Along with NOAA,UCAR(NetCDF,Unidata,CF),ISO,W3 websites, I have also found
> those of IOOS and PACIOOS instructive helpful.
> I have been tasked with creating MetaData for a number of products created
> or used at http://cw3e.ucsd.edu .
> To begin with, I am focusing on WRF model output and the MI_Metadata
> template. I hope that the metadata
> will lean in the direction with what I sense to be evolving standards, at
> least in the earth sciences
> community.
> I used `ncdump -h` header information and NetCDF_ToolsUI_4.6 ncgm output to
> assist in populating the MI_Metadata entities.
> In the process I used oXygen and (github) ncISO2.0/UnidataDD2MI.xsl to
> transform the ncgm into xml .
> Regarding variable units, the xml is populated with entries like:
> <gmd:units xlink:href="http://example.org/someUnitsDictionary.xml#mm"/>
> At this stage in my evolving understanding of ISO, NOAA, and UCAR
> conventions
> I perceive it would be beneficial to change these links to cite
> udunits2-*.xml files
> e.g.  https://www.unidata.ucar.edu/software/udunits/udunits-
> current/udunits/udunits2-prefixes.xml
> I started to invent the wheel writing scripts to parse and match model
> units to udunits entities
> ... and eventually realized the scope and subtleties involved.
> Simple issues:  the WRF model units are inconsistent, e.g. regarding
> denominators vs negative
> exponents, the use/meaning of blanks space, ...
> Additional complexity exists in the way udunits handle unit sub components,
> e.g. scaling
> prefixes in the file above, being separate from other components of a unit,
> the two of
> which would commonly be combined in model output metadata.
> Generally matching the plethora of potential aliases to base/common/derived
> units.
> I searched for potential udunits2 tools and found links such as
> https://www.unidata.ucar.edu/software/udunits/udunits-2.0.4/udunits2lib.html
> I have seen metadata which lacks unit dictionary references and wonder if
> I am attempting to take on too much for a novice.  Admittedly at this stage
> my head is swimming and the degree to which certain pieces of information
> are necessary to satisfy conventions (vs desirable to include) is still
> not completely clear.
> Can anyone recommend a way forward?  A units parsing/processing tool ?
> Or advice as to how to handle the units issue more simply but with an
> eye to evolving conventions?   (A state of the art yet eloquently simple
> summary of any of the issues addressed herein :) )
> (Of course, the local powers of be want all this yesterday)
> Thanks for your time and any potential input!

Steve Emmerson

Ticket Details
Ticket ID: PIK-524714
Department: Support UDUNITS
Priority: Normal
Status: Closed
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