I think that the important factor in the text posted by Jonathan:
'''Generic applications should treat the data as missing where any
auxiliary
coordinate variables have missing values; special-purpose applications
might
be able to make use of the data.'''
is that it puts the onus on interpretation on the downstream
application, with some advice; this is better than requiring the data
provider to
I feel that having the capability to have missing data stored in
auxiliary coordinates is important. Whilst the interpretation of the
meaning of such encoding needs some care, I feel that the specification
should not be too restrictive on this.
I have a use case to consider:
Phenomena as Auxiliary Coordinates
The distinction between a data variable and an auxiliary coordinate
can often be quite an arbitrary one.
A data variable may be used as an auxiliary coordinate for another
data variable which shares the same coordinate variables.
Consider - coordinates x, y, z and t
- relative humidity data with respect to x, y, z and t:
- pressure data with respect to x, y, z and t
I would not want to alter the specific humidity data in any way as
a result of adding the pressure data as an auxiliary coordinate.
A post processing application may choose:
- to interpret the pressure data auxiliary coordinate missing
data as missing data indicators for the relative humidity data to enable
data regridding onto specified pressure levels;
- to compute the variability of the humidity measurements,
ignoring the pressure data;
these are operational choices, made by the software.
I think CF should enable data to be stored to enable such processes to
take place, and not mandate that one or other storage method is correct.
-----Original Message-----
From: cf-metadata-bounces at cgd.ucar.edu on behalf of Jonathan Gregory
Sent: Sat 31/03/2012 21:19
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] CF-1.6 Conformance
Requirements/Recommendations
Dear all
John Caron proposed
> "Applications should treat the data as missing where the auxiliary
coordinates are missing"
and Steve proposed (an hour later, I think)
"Application writers should be aware that under some (rare)
circumstances data auxiliary coordinate values may be missing, while
other parameters at the corresponding indices remain valid. While
special purpose applications may be able to glean useful information
at these indices, most applications will want to regard data as
missing where the auxiliary coordinates are missing "
I could agree to either of these. I prefer John's, because it is
simpler, but
it's more severe than Steve's. A compromise might be possible, e.g.
Generic applications should treat the data as missing where any
auxiliary
coordinate variables have missing values; special-purpose applications
might
be able to make use of the data.
Any good?
Cheers
Jonathan
_______________________________________________
CF-metadata mailing list
CF-metadata at cgd.ucar.edu
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
Received on Mon Apr 02 2012 - 10:53:05 BST
