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, Günther" 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,
Günther Lang
Bundesanstalt für Wasserbau
Abteilung Wasserbau im Küstenbereich
Referat Ästuarsysteme II (K3)
Wedeler Landstraße 157
22559 Hamburg, Germany
phone +49 40 81908 360
mail [email protected]
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--
Rosalyn Hatcher
NCAS Computational Modelling Services
Dept. of Meteorology, University of Reading,
Earley Gate, Reading. RG6 6BB
Email: [email protected] Tel: +44 (0) 118 378 6016
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