John & CF-ers,
Since CF 1.0 doesn't have conventions for specifying the spheriod, let's
make sure they are there in the next release! We want GIS tools like
ArcGIS to get the geospatial information they needs from a CF-compliant
file without a user filling in extra metadata by hand.
That's what we are aiming for, right? This means we should have
conventions for specifying vertical datums (geoids) as well.
Check the bottom of this page <
http://tinyurl.com/64mlx> for
an example of coordinate system specifation in WKT (Well Known Text) for a
3D compound coordinate system (using the Airy 1830 spheriod, Transverse
Mercator projection, and Newlyn vertical datum.)
BTW, if there are folks out there wondering what this fussing is about,
there is an excellent short guide to coordinate systems at
<
http://www.gps.gov.uk/guide1.asp> which speaks plain english, but doesn't
dumb things down too much.
-Rich
Dr. Richard P. Signell rsignell at usgs.gov
U.S. Geological Survey (508) 457-2229
384 Woods Hole Road Fax: (508) 457-2310
Woods Hole, MA 02543-1598
-----cf-metadata-bounces at cgd.ucar.edu wrote: -----
To: cf-metadata at cgd.ucar.edu
From: John Caron <caron at unidata.ucar.edu>
Sent by: cf-metadata-bounces at cgd.ucar.edu
Date: 02/02/2005 08:25PM
Subject: Re: [CF-metadata] proposed UTM projection
Rich Signell wrote:
>
> John Caron wrote:
>
>> Theres 2 parts:
>>
>> 1) Transverse Mercator doesnt specify the ellipsoidal parameters,
>> presuming i suppose a spherical earth. Im working with a dataset
>> where im told the ellipsoidal form is needed for accuracy..
>
>
> There are projections, and there are spheroids. You can use any
> projection with any spheroid. UTM is now most commonly used with the
> WGS84 spheroid, but has and can be used with any of them! Look at
> any (decent) map and it will tell you both the projection and the
> datum (which implies a spheroid).
Yep. But CF has no conventions for specifying the spheroid :^(
>
>>
>> 2) The UTM zone specification is in wide use, and is a shorthand for
>> all the other TM parameters.
>>
>
> Ok. So how about we add an attribute that specifies the UTM zone
> instead of a whole new projection.
possible; but then you should specify TM params OR zone, so that has to
be made clear.
either way is fine, what do the PTB (powers that be) think?
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Received on Wed Feb 02 2005 - 20:53:19 GMT
