> 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: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of John Caron
Sent: 01 February 2011 19:40
To: cf-metadata at cgd.ucar.edu; 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
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Received on Wed Feb 02 2011 - 09:16:46 GMT
