[CF-metadata] CF-1.6 Conformance Requirements/Recommendations

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 26 Mar 2012 15:48:29 +0100

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
Received on Mon Mar 26 2012 - 08:48:29 BST