Hi again, I must admit that your data is very different to the types of data I work with and I don't fully understand issues with composite images. Typical data for me are time series where a series of parameters, including position are logged every 30 seconds or so as a ship sails along. Years ago I had a dataset where a form of local time (ship's time) was used and they switched from daylight saving part way through the cruise. Result was that according to the data the ship was in two different places at a given time: not good. If a ship sails across the Atlantic, we don't want the time channel jumping around as time zone boundaries are crossed. We have a lot of this type of data assembled over the past 30 years - not just ships but also moored instruments - with elapsed time channels that are assumed to be UT and have put much effort in the past into the conversion of any incoming local times in both data and metadata to UT. To suddenly have this interpreted as local wouldn't im prove the accuracy of anything!
Making the default CF time local might make the standard appear more robust for your data world but not for mine. Alignment with ISO standards is an essential requirement for the development of new conventions, but I don't feel retrospective adoption to be a prudent path. Cheers, Roy. ________________________________________ From: cf-metadata-boun...@cgd.ucar.edu [cf-metadata-boun...@cgd.ucar.edu] On Behalf Of Julia Collins [colli...@nsidc.org] Sent: 22 October 2010 17:32 To: cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] Interpretation of unspecified time zone (was: New standard names for satellite obs data (timeas ISO strings)) Hi, On Fri, 22 Oct 2010, Lowry, Roy K wrote: > I wonder how many existing CF data files would have the meaning of their > time channel changed were this suggestion to be adopted. I am sure many. In some cases it might even make them accurate. :-) At some level, it's a tradeoff between "breaking" existing data descriptions and creating a more robust standard. Whether my suggestion creates a more robust standard or not is up for debate. It does align it more closely with the ISO standard, and I think there's something to be said for that. > If I were Julia I would be reworking my data so that the time channel was > true UT. I've had so many problems in the past with local time > co-ordinates........ It's not data I'm generating, but rather data provided by a PI who has determined that this is how he wants to present his data. I believe the idea is to be able to view a wide geographic area over the same effective local time. It's a composite image. If you can tell me how to represent these multiple UTC times for one variable using the existing CF conventions, then I'll try to do so. I believe CF limits me to specifying one time zone for a particular time dimension. Re-working the data so that it's broken up into separate time zones would, as I understand it, mean splitting up the data variable into multiple variables, each with their own time dimension, which is not what the data provider wants to do. Splitting the variable would require the user to put the pieces back together in order to see the image as the data provider intended. As far as I can tell, following the ISO interpretation of the time zone indicator does exactly what I need without ambiguity. I'd like to describe the data in a way that's perfectly compliant with the CF convention, but in this case I don't see a way to do so. Thanks, Julia -- Julia Collins National Snow and Ice Data Center http://nsidc.org/ colli...@nsidc.org +1 303.492.6405 _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata -- This message (and any attachments) is for the recipient only. NERC is subject to the Freedom of Information Act 2000 and the contents of this email and any reply you make may be disclosed by NERC unless it is exempt from release under the Act. Any material supplied to NERC may be stored in an electronic records management system. _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
