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[CF-metadata] Ancillary variables in coordinate variables (latitude, longitude, ...)

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 6 May 2015 18:09:31 +0100

Dear Kristian

> In these case the feature type is a trajectory, so
> the latitude and longitude are auxiliary coordinates.
>
> You said that for auxiliary coordinates it could be ok, Would this mean
> that it could be added to the CF conventions?

I don't think any change would be needed to the CF convention. CF allows a
given netCDF variable to serve as both a data variable in its own right and
an aux coord var of another data variable. An example of where this might be
useful is for an ocean model on density levels, in which depth as a function
of density is of interest as a data variable, but could also be an auxiliary
coordinate variable for other data variables. Therefore I think it would be
legal for your aux coord vars to have ancillary vars. Since the lat and lon
along a trajectory are actually dependent data variables, this feels quite
reasonable to me for your case. I wonder what others think.

Cheers

Jonathan

> On 5 May 2015 at 18:58, Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
>
> > Dear Kristian
> >
> > Ancillary variables are only for data variables in the current convention.
> > It wouldn't be illegal to use the attribute on coord variables, but CF
> > doesn't define what that would mean. (CF always permits any
> > non-standardised
> > attributes.)
> >
> > I wonder whether these are 1D coord variables (in the Unidata sense) or
> > aux coord vars (named by the coordinates attribute)? In the latter case, it
> > could be OK, because other data variables could be named as aux coord vars.
> >
> > Best wishes
> >
> > Jonathan
> >
> >
> > ----- Forwarded message from Kristian Sebasti??n <ksebastian at socib.es>
> > -----
> >
> > > Date: Thu, 30 Apr 2015 08:43:54 +0200
> > > From: Kristian Sebasti??n <ksebastian at socib.es>
> > > To: cf-metadata at cgd.ucar.edu
> > > Subject: [CF-metadata] Ancillary variables in coordinate variables
> > (latitude,
> > > longitude, ...)
> > >
> > > Dear CF community,
> > >
> > > We have some dataset with quality controls applied to the coordinate
> > > variables, such as latitude and longitude coordinate. The result are
> > > quality control variables that we associate as ancillary variables of the
> > > coordinate variables with the ancillary_variables attribute. For example,
> > > the LAT coordinate variable has the ancillary variable QC_LAT. The
> > dataset
> > >
> > http://thredds.socib.es/thredds/dodsC/drifter/surface_drifter/drifter_svp052-ime_svp017/L1/2014/dep0001_drifter-svp052_ime-svp017_L1_2014-05-25.nc
> > >
> > > The cf-conventions clarifies the use of the ancillary_variables attribute
> > > for data variables but not for coordinate variables. My question is, Is
> > the
> > > ancillary_variables attribute in coordinates variables compliant with the
> > > cf-conventions?
> > >
> > > Best regards,
> > >
> > > Kristian
> > >
> > > --
> > >
> > > Kristian Sebastian Blalid
> > > SOS Division: Data Center Technical
> > > Tel: 971439860 - Fax: 971439979
> > > E-mail: kristian.sebastian at socib.es
> >
> >
> >
> > > _______________________________________________
> > > CF-metadata mailing list
> > > CF-metadata at cgd.ucar.edu
> > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> >
> >
> > ----- End forwarded message -----
> > _______________________________________________
> > CF-metadata mailing list
> > CF-metadata at cgd.ucar.edu
> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> >
>
>
>
> --
>
> Kristian Sebastian Blalid
> SOS Division: Data Center Technical
> Tel: 971439860 - Fax: 971439979
> E-mail: kristian.sebastian at socib.es



----- End forwarded message -----
Received on Wed May 06 2015 - 11:09:31 BST

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