Dear all
Brian has a good point that sect 5.3 allows that there might be missing data
in aux coord variables. Appendix A - which is equally ancient in the story of
CF :-) - is not consistent with this, because it didn't allow _FillValue or
missing_value atts for coordinates until sect 9 was introduced in version 1.6.
But never mind the history, the point is to clarify what we need now.
In Randy's, Rich's and Bert's examples, if I understand correctly, there are
non-existent points, at which both data and aux coord vars are missing values.
That is also what sect 9 requires. I don't see any problem with this.
Nan's example is different, because it has missing values in aux coord vars
at points where there is non-missing data. If we all agree that this is OK
too, then fine. Speaking for myself, I could agree to it, but I'm less happy,
because clearly the aux coord var is not doing its job of locating the data.
I think you said, Nan, that you might fill them in at some later stage. At
that stage, they should certainly be aux coord vars. Before they are filled
in, of course I am not saying they should be excluded from the file, but I
am asking if they should be regarded as data, rather than coordinates. A
pressure value which was destined to be an aux coord var, but is actually a
data variable measured by a sensor and has missing values in it, could be
named by the ancillary_variables attribute. It is really per-point metadata,
which is what ancillary_variables are
(
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/cf-conventions.html#ancillary-data)
but you could argue it should not be regarded as an aux coord var if it can't
provide information for every point where there is data.
I'm just asking. I don't have a very strong opinion about this, but I'd like
to know if others have the same concern that I do.
My existing ticket (85) connected with this subject is a defect ticket. It
is only able to correct mistakes. It can't make a substantive change to the
convention, just clarify it. If we can decide easily how to clarify it, that
is fine. I'll amend the ticket if we have a clear decision. Otherwise, we
should use a different ticket.
Best wishes
Jonathan
Received on Wed Mar 28 2012 - 06:26:42 BST
