Hi Jon, Thanks for the helpful summary :) We have had similar issues with handling data that represents time periods, and it'd certainly be good to find some way to address that.
On 21/10/10 15:28, Jon Blower wrote: > 1. Steve and Roy both asked (I think) why we can't have a more general > notion of precision that applies to all coordinate axes, not just time. > I argue that precision in time *can be* (but is not always) different > semantically. When I say "these data are representative of June 2009" I > don't mean "these data were collected on the 15th of June 2009, plus or > minus 15 days". The concept of "data representative of a time period" > is very different from "data collected at an uncertain time". > "Representative" data is commonly found in high-level analysed products, > not so much in instrument records I guess. That raises an interesting point - perhaps accuracy and representativeness are getting bundled together into precision in this discussion, and should instead be considered separately? For example, a satellite might pass over an area once a day, taking about 10mins to cover it. The accuracy of a seconds-since-epoch timestamp at the center point might then be +/- 5mins (with a precision of 1 second) but the data for that timestamp might be considered to be representative of the whole day as there is no more coverage. This accuracy / representativeness split would apply equally to other coordinate types as well as time - for example, a satellite pixel coordinate has a accuracy based on the quality of the geolocation (e.g. 100m) but represents a much larger area (e.g. 1km square). One could encode both accuracy and representativeness in one field by making the precision of a timestamp imply representativeness, but that loses some of the semantics above. Without wishing to get into too much of a tangle on the issue, perhaps there's a case for improving CF's description of both accuracy and representativeness [of coordinates]? Cheers, Mike. -------------------------------------------------------------------------------- Plymouth Marine Laboratory Registered Office: Prospect Place The Hoe Plymouth PL1 3DH Website: www.pml.ac.uk Registered Charity No. 1091222 PML is a company limited by guarantee registered in England & Wales company number 4178503 -------------------------------------------------------------------------------- This e-mail, its content and any file attachments are confidential. If you have received this e-mail in error please do not copy, disclose it to any third party or use the contents or attachments in any way. Please notify the sender by replying to this e-mail or e-mail [email protected] and then delete the email without making any copies or using it in any other way. The content of this message may contain personal views which are not the views of Plymouth Marine Laboratory unless specifically stated. You are reminded that e-mail communications are not secure and may contain viruses. Plymouth Marine Laboratory accepts no liability for any loss or damage which may be caused by viruses. -------------------------------------------------------------------------------- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
