Hi again.
OK, after our earlier discussion about auxiliary coordinate variables, this
sure looks like a source or institution variable shouldn't be an auxiliary
coordinate variable. It is not remotely related to a coordinate axis is
it? Shouldn't you be talking about this as an ancillary variable? Or is
this being used as a label coordinate so that you can make plots that show
values across sources?
If we are going to do this for these two global attributes, shouldn't we go
ahead and do it for all other global attributes?
Grace and peace,
Jim
On Thu, Mar 29, 2012 at 10:55 AM, Jonathan Gregory <
j.m.gregory at reading.ac.uk> wrote:
> Dear Nan
>
> > It seems that, to indicate various sources for different variables
> > within a file,
> > one would use institution as a variable attribute instead of a
> > global. This is
> > the approach that NODC has used in their new NetCDF templates.
>
> That is already legal in CF. The source and institution are allowed as
> global
> or variable attributes.
>
> If source and institution become legal standard names, it means they can be
> used as the values of string-valued scalar or auxiliary coordinate
> variables.
> A scalar string coordinate variable is just a string (a 1D char array), so
> it
> would be functionally equivalent to a variable attribute. However, it could
> be an array of strings i.e. a 2D char variable, as you say:
>
> > is this meant
> > to be a 2D variable? It makes a lot of sense in that context.
>
> You could use this if the data had a dimension which corresponded to a
> source
> or institution e.g.
>
> dimensions:
> ninst=10;
> lat=180;
> lon=360;
> stringlength=30;
> variables:
> float ppn(ninst,lat,lon);
> ppn:standard_name="precipitation_flux";
> ppn:units="kg m-2 s-1";
> ppn:coordinates="institution";
> char institution(ninst,stringlength);
> institution:standard_name="institution";
> data:
> institution="GFDL", "MPI", "CSIRO", ...;
>
> Here, institution is an auxiliary coordinate variable.
>
> As you say,
>
> > this should
> > either be dimension (1) or share a dimension with one of the coordinates?
>
> This is described in sect 6.1 of the convention.
>
> Best wishes
>
> Jonathan
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>
--
Jim Biard
Research Scholar
Cooperative Institute for Climate and Satellites
Remote Sensing and Applications Division
National Climatic Data Center
151 Patton Ave, Asheville, NC 28801-5001
jim.biard at noaa.gov
828-271-4900
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