Dear Guenther,
Looking in the CF Convention it's not stated that using auxiliary
coordinate variables with compression by gathering is not valid.
In your Example 2 the CF checker has not recognised, in the checking of
the auxilliary coordinate variables, that datapoint is a compressed field.
I think you're probably the first person to try doing this. So assuming
everyone is happy that this is valid in the CF Convention,
I will modify the CF Checker to look for compressed dimensions when
checking the dimensions of an auxiliary coord variable.
Regards,
Ros.
On 28/04/11 15:49, "Lang, G?nther" wrote:
>
> Dear CF metadata discussion group.
>
> Salinity data given at several arbitrarily spaced locations in
> different depth layers shall
> be stored in a NetCDF file using a compressed dimension (datapoint) to
> remove permanently
> missing data from the data record.
>
> In order to get used to this style of data storage I have prepared two
> example CDL sets.
>
> With NCGEN the respective NetCDF data files were generated from the
> CDL files and
> verified using checker program
> http://puma.nerc.ac.uk/cgi-bin/cf-checker.pl .
>
> Example 1 - compression by gathering using true coordinate variables:
>
> * see attached files test_compress_true_coord_var.cdl | .nc .
> * checker says: ok, CF compliant .
>
> Example 2 - compression by gathering using auxiliary coordinate
> variables for the horizontal:
>
> * see attached files test_compress_aux_coord_var.cdl | .nc .
> * checker says: not ok, due to
> * ERROR (5): Dimensions of node_lon must be a subset of dimensions
> of salinity_3d
> * ERROR (5): Dimensions of node_lat must be a subset of dimensions
> of salinity_3d
>
> From my understanding the dimensions of the auxiliary coordinate
> variables NODE_LON
> and NODE_LAT are a true subset of the (uncompressed) dimensions of
> salinity_3d, similar
> to the above example 1.
>
> Due to the fact that the only difference lies in the use of auxiliary
> coordinates
> for the horizontal domain, my question is whether within example 2
> there is a
> true error concerning the CF compliant description of this data set or
> whether
> it is not possible at all to store data like example 2 in a CF
> compliant compressed
> NetCDF file.
>
> Any helpful remarks welcome.
>
> Yours sincerely,
>
> G?nther Lang
> Bundesanstalt f?r Wasserbau
> Abteilung Wasserbau im K?stenbereich
> Referat ?stuarsysteme II (K3)
> Wedeler Landstra?e 157
> 22559 Hamburg, Germany
> phone +49 40 81908 360
> mail guenther.lang at baw.de
>
>
> _______________________________________________
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> CF-metadata at cgd.ucar.edu
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--
Rosalyn Hatcher
NCAS Computational Modelling Services
Dept. of Meteorology, University of Reading,
Earley Gate, Reading. RG6 6BB
Email: r.s.hatcher at reading.ac.uk Tel: +44 (0) 118 378 6016
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Received on Wed May 04 2011 - 06:43:36 BST
