> 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
[mailto:cf-metadata-bounces@xxxxxxxxxxxx] On Behalf Of John Caron
Sent: 01 February 2011 19:40
To: cf-metadata@xxxxxxxxxxxx; 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
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.
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