Hi Jonathan,
Thanks, for your reply and from others in the CF community.
I certainly have had lots of responses on this topic, all useful information.
I appreciate your deep knowledge of the CF standard which often
clarifies the best way to do things.
Actually I am not 100% clear about use of "auxilliary co-ordinate variables" and
the "coordinates" attribute. Some questions:
1) What distinguishes an 'auxilliary coordinate variable' from a plain old
'coordinate variable'?
2) Is it permissable for a 'auxilliary coordinate variable' to have either the
scalar form
e.g "float lat" or the array form lat(lat) with lat=1 declared as a dimension?
3) Do we need the coordinates attribute to "look-up"
the corresponding auxilliary cordinates variable? For example if we had a
variable declared as salinity(z) then to look up its lat, long and time
coordinates for say display purpose
would the "salinity:coordinates = "lat long time"" attribute used for the
lookup.
4) However if we had the salinity variable be declared as
salinity(lat,long,time,z) then
the application would lookup the co-ordinates from the co-ordinates variables
declaration names
and we wouldn't need the salinity:coordinates attribute?
I do notice that a lot of the netCDF CTD data out there doesn't use the
coordinates
attribute. Is this a feature that came in later with CF v1.5 or v1.6?
Regards,
Andrew
PS: To clarify, the netCDF CTD data we produce will have monotonic pressures.
The raw data we get in may go up/down due the motion of the CTD instrument.
----- Original Message -----
From: "Jonathan Gregory" <j.m.gregory at reading.ac.uk>
To: <cf-metadata at cgd.ucar.edu>
Sent: Wednesday, April 04, 2012 12:47 AM
Subject: Re: [CF-metadata] Ocean CTD data following CF Conventions v1.6
> Dear Andrew and Nan
>
>> If your pressure isn't monotonic, and so can't be a coordinate
>> variable, I don't know
>> whether it's preferable to demote ALL the coordinates to auxiliary
>> coordinate variable
>> status,
>> TEMPERATURE: coordinates = "TIME,PRESSURE,LATITUDE,LONGITUDE" ;
>
> I don't think there's a recommendation to treat the coordinates in the same
> way. If size-1 coordinates are listed in the coordinates attribute, it is also
> permissible to make them scalar variables and not define the size-1 dimension.
> These are CF scalar coordinate variables. e.g.
>
> float lon;
> float lat;
> float time;
> float temperature(pressure);
> coordinates="lat lon time";
>
> where all the variables should have units and standard_names as usual. It
> doesn't matter what order is used for the coordinates attribute. Note that
> it's a blank-separated list (not comma-separated).
>
> Best wishes
>
> Jonathan
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Received on Tue Apr 03 2012 - 20:29:45 BST
