Hi Jonathan -
For underway CTD profiles (gliders and floats, too, I'd think) if the
pressure
sensor fails intermittently, you can approximate Z by interpolating over
time, assuming there are good values along the track. In "final" data,
we might
do that, but we might like to present raw data in CF files, too. So,
yes, this data
would be useful, with fill values here and there in the pressure record.
Are we getting into a grey area that might be outside the scope of the CF
standard - judgements made about the usefulness of data? Having all your
coordinates seems like an excellent NetCDF "best practice" and could
certainly
be a "rule" for many tools, but it could preempt the use of the CF
standard for
some kinds of observational data.
Cheers -
Nan
On 3/26/12 10:48 AM, Jonathan Gregory wrote:
Dear Nan and John
It's a good thing we're having this discussion! In my understanding, we have
always prohibiting missing data in aux coord vars, and in section 9 we
explicitly allowed for the first time. Evidently we should be clear, one way
or the other (which was one of the intentions of the defect ticket I opened).
The restriction on coord vars not having missing data is, I think, hard to
avoid because they are required to be distinct and monotonic.
In Nan's case:
For something like towed CTD data, you might have a period of time where
data from the pressure sensor is missing. If neither the coordinate or aux
coordinate can contain null values, does this mean the only options are
interpolating Z or removing that section of data?
When the sensor is missing, does that mean the data can't be geolocated? As
you know, geolocation is one thing CF tries hard to do. Is the data useful if
you don't know where it comes from? Perhaps you know in some other way?
In John's case
Consider a geosynch satellite with lat/lon aux coordinates. the
nature of the image is that there are many points around the outside
of the image that are not located on the earth. i dont see any good
choices other than to put missing values there for lat/lon..
Bert has coincidentally mentioned a similar case (not on the list). I tend to
agree that if index space contains locations that simply do not exist, you
could put missing data in aux coord vars, but I think this needs a change to
the CF convention.
To add insult to injury, it seems possible that there are valid data
values at these locations. Not sure about that however. Can anyone
with geosynch data expertise comment?
As in Nan's case, I am curious about how the data can be useful if it doesn't
have a location.
Best wishes
Jonathan
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