Dear Etienne
I think the structure you have adopted for the data is fine.
> double pft(pft) ;
> pft:long_name = "plant functional type" ;
> pft:units = "none" ;
>
> double npp(time, pft, latitude, longitude) ;
> npp:long_name = "npp of carbon for each pft" ;
> npp:units = "kg m-2 year-1" ;
The specific problem you raise is concerned with the axis attribute. That
attribute is really intended for identifying spatiotemporal coordinates;
although it may be convenient, it is redundant because they can also be
identified in other ways. It has not been extended for non-spatiotemporal
axes like pft. In your CDL, the pft axis is identified by its long_name.
To make this more reliable, you might want to use a standard_name for this
pft coordinate variable. There isn't such a standard_name at present, but
area_type is often vegetation type in practice, so you could perhaps use
that. We could standardise new area_types by proposals to this email list.
Also, there is the new proposal, which I expect will go into the
standard_name table, for UN/FAO land cover types, which in many cases are
also vegetation types.
See
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2012/033507.html
The quantities identified by these standard_names are string-valued, whereas
you expect a numeric pft. However, a string-valued one could be encoded as a
number by using the flag_values and flag_meanings attributes.
There is an existing standard name for NPP as well viz
net_primary_productivity_of_carbon (kg m-2 s-1)
Best wishes
Jonathan
Received on Mon Jun 04 2012 - 11:17:43 BST
