On 3/29/2012 10:11 AM, Rich Signell wrote:
Folks,
I'm confused now. Are we proposing that we could have CF-compliant
files that have no valid coordinate data, with the justification that
somebody may figure the coordinates out later?
Hi Rich,
I'm afraid that this is the tip of an iceberg as we begin to try to
acknowledge the differing viewpoints of observations versus models and
products. It would clearly be wrong to say to an observation program
that it cannot include temperature and salinity measurements in their CF
files, because the pressure sensor failed at that point. While the
resulting observations have greatly diminished value (and maybe
ultimately prove to have no value at all), it would be wrong to throw
the measurements away. This is in the same spirit that it is preferable
to _flag_ QC evaluations of "bad data" rather than throw them away.
Should CF approach this head-on? For example, CF could stipulate that
IFF a data provider wants to include valid observations at points where
auxiliary coordinates are missing, they must also include some kind of
flag variable as well. To me this seems unnecessary. It is sufficient
simply to state that under some circumstances there may be valid values
at indices where auxiliary coordinates contain missing values -- perhaps
adding that the circumstances will be rare and application-specific.
Crystal ball: Meeting the sometimes-conflicting needs of observations
and models/products is going to lead to more of these discussions.
- Steve
-Rich
On Thu, Mar 29, 2012 at 1:01 PM, Steve Hankin<[email protected]> wrote:
Returning to Nan's valid example, the proposed wording isn't very attuned to
the valid needs of (in situ) observations. If the pressure sensor fails,
while other sensors remain active, then the Z auxiliary coordinate becomes
unknown but other parameters remain valid. The observations have
potential value (though greatly degraded, of course), because a future
investigator may figure out how to estimate the Z position from other
information. For the investigator writing those applications, the
statements below are wrong or misleading.
I think the right thing to say is something along the lines of
"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 "
On 3/29/2012 9:05 AM, Jim Biard wrote:
All,
For the work I am doing right now, I am required to not fill in missing
values in any variable. I encourage everyone to go with John Caron's idea.
Grace and peace,
Jim
On Thu, Mar 29, 2012 at 12:01 PM, John Caron<[email protected]> wrote:
To answer this concern, I would agree to modify the statement
"Applications are free to assume that data is missing where the auxiliary
coordinates are missing"
to
"Applications should treat the data as missing where the auxiliary
coordinates are missing"
My concern is that we shouldnt make a file "non CF compliant" just because
the data provider would like to store data values where there arent
coordinate values. But telling them that standard software _will_ ignore
them seems good.
On 3/29/2012 9:47 AM, Rich Signell wrote:
Jonathan,
+1 on your idea of only identifying variables as aux coordinate
variables once they have valid values at valid data locations.
-Rich
On Thu, Mar 29, 2012 at 11:32 AM, Jonathan Gregory
<[email protected]> wrote:
Dear Jim
We are discussing auxiliary coordinate variables. They do not have to be
1D or monotonic. Those requirements apply to coordinate variables in the
Unidata sense. CF distinguishes these two concepts in Sect 1.2.
The point is, the information in the variable *is* coordinate
information,
I would say, if it's missing, it's not information.
What if we say something along the lines of, "Applications should treat
the
data as missing where the auxiliary coordinates are missing when
plotting
data."? Would that resolve the problem?
Plotting is not the only thing that an application might wish to use it
for.
If we said, more generally, "Applications should treat the data as
missing for
all purposes where the aux coord variables are missing", it would be
almost
the same as not allowing missing data in aux coord vars, since there
would be
no point in providing a data value if it was not permitted to use it.
Although I am arguing one side, I could be convinced either way. But it
does
feel unsafe to me at present.
Cheers
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
[email protected]
828-271-4900
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