I have to agree with Jon on this one. To borrow his phrase, I wouldn't want to be "inventing metadata".
Regarding the problem of spherical models using uncorrected WGS84 positions - two wrongs don't make a right. It's the use of the models that need fixing. Altering the interpretation after the fact just compounds the problem. And since using WGS84 positions on a spherical model is tantamount to altering the model physics, who knows ... maybe correcting the positions would give more accurate results from the model. Richard Hattersley AVD Expert Software Developer Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom Tel: +44 (0)1392 885702 Fax: +44 (0)1392 885681 Email: [email protected] Website: www.metoffice.gov.uk -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jon Blower Sent: 02 February 2011 16:17 To: John Caron; [email protected]; Java NetCDF Subject: Re: [CF-metadata] ESRI implementation of ellipsoidal-earth > Also, they are wondering what to use for the default ellipsoid when these are not specified. It seems to me the obvious > candidates are 1) spherical earth with a standard radius, or 2) WGS84 ellipsoid. My inclination would be to treat the lack of datum as an issue to be escalated to the user to choose what to do. Seems more complicated but I'd be very wary of "inventing metadata" for the sake of convenience. Maybe ESRI could provide the user with a global "datum leniency" setting, that a user could explicitly set to avoid being bothered by prompts, if they know what they are doing. It's less of an issue for viewing datasets in isolation, or for coarse-resolution data. But for high-resolution (regional- and local-scale) data the datum shift can be significant. I see this increasingly with people doing data assimilation in small-scale models - the geolocation error can be greater than the size of a grid cell. (I will declare my own hypocrisy and note that ncWMS does assume WGS84 at the moment (it won't soon)... but that's how I came across the problem in the first place!) HTH, Jon -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John Caron Sent: 01 February 2011 19:40 To: [email protected]; Java NetCDF Subject: [CF-metadata] ESRI implementation of ellipsoidal-earth Apparently ESRI is willing to add support for CF 1.5 grid_mapping attributes for ellipsoidal-earth/geodetic-datum definitions in the Grid Mappings and Projections specification. They are looking for sample data, especially using ellipsoidal parameters (semi_major_axis/semi_minor_axis/inverse_flattening). Does anyone have any? Also, they are wondering what to use for the default ellipsoid when these are not specified. It seems to me the obvious candidates are 1) spherical earth with a standard radius, or 2) WGS84 ellipsoid. Opinions? John _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
