Dear Martin
I feel there would be an advantage in flexibility, by not requiring the missing
data count to be the first bin necessarily. The new attribute could indicate
the index of the bin which contains the missing data count. I suggest that
this would be an attribute of the coordinate variable of the histogram for the
quantity which is binned (cloud top height), since the index refers to that
dimension specifically.
I agree it would be neat if it were possible instead to put _FillValue in the
coordinate variable. Actually _FillValue is not allowed in coordinate vars by
CF, so as far as CF is concerned it would not be a problem to adopt this as a
new convention. But maybe software would have problems with it. If we need the
new attribute, I'd suggest missing_value_index, to make it more similar to
missing_value and _FillValue. What would you put in the coordinate and bounds
for the missing data bin?
In any case, this needs a new convention to be proposed as a trac ticket.
Best wishes
Jonathan
----- Forwarded message from martin.juckes at stfc.ac.uk -----
> Date: Tue, 11 Oct 2016 12:41:21 +0000
> From: martin.juckes at stfc.ac.uk
> To: cf-metadata at cgd.ucar.edu
> CC: rojmarch at u.washington.edu
> Subject: [CF-metadata] Missing data bins in histograms
>
> Hello,
>
> the CF standard name list has two "histogram_.... " entries, and in the CMIP6 data request we may need to add a third, a histogram_of_cloud_top_height. Besides the standard name, we also need, for this new variable, a method of encoding the "missing data" bin in the histogram. That is, the histogram should record frequency in 16 data bins and one additional bin for the frequency of missing data.
>
> Can we define a "missing_data_index" attribute for histogram variables, and use this to indicate that the first bin in the array has this special purpose. It might be more pythonic to put the _FillValue in the coordinate value for the missing data bin, but I suspect that this would cause substantial problems for many software packages.
>
> regards,
> Martin
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----- End forwarded message -----
Received on Tue Oct 11 2016 - 11:17:06 BST
