This has a good description of UTM coordinates
http://ergodd.zoo.ox.ac.uk/eden/etc/helpfiles/EDENHELPGPS.pdf
Alan Harris
Glenn Waldron wrote:
On Wed, Jun 11, 2008 at 9:12 AM, Jean-Sébastien Guay
<[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Hi Glenn,
Thanks for the links, combined with Chris and Alan's links I might
get a better understanding of the general terminology and
concepts... That's one thing I'm lacking now, it just sounds like
a bunch of acronyms and alien words to me :-) I thought being in
computer science I'd be immune to acronymitis by now...
Anyway the first task is to figure out whether you need to
reproject your data at all. UTM is a flat-earth XYZ system. Do
you have a terrain? What spatial reference system is it in?
We /will/ have a terrain, but I don't have details on it. If it's
also in UTM, we could use it directly and just not reproject
anything, right?
Right.
So you're saying we could just, for example, decide that our world
origin is at some translation from the UTM coordinates' origin,
and then translate all the data we get by that, and be done with it?
Right. Or better yet, use a MatrixTransform to place your terrain at
actual UTM coordinates, and theyn you don't even have to translate the
incoming data.
For example, from the specs document I've got, it seems the
coordinates we might get would look like
576120.324, 6224420.858, -102.73
What units would that be in? Our models are modeled in meters, and
we'd like to use meters as world-units, so for distances to look
right would we need to scale the terrain and the position data we get?
UTM coordinates are in meters.
X is relative to the central meridan of the UTM zone, plus the "false
easting", which exists only to avoid the use of negative numbers.
Y is relative to the equator. Y values in the southern hemisphere are
also given a "false northing" to avoid negative #s.
Still a bit of confusion about the basic concepts. I'll go read
those links now :-)
Bottom line: if you use VPB to build a terrain in UTM zone 32 (or
whatever), you will need to do no coordinate conversion.
J-S
--
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Jean-Sebastien Guay [EMAIL PROTECTED]
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http://www.cm-labs.com/
http://whitestar02.webhop.org/
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Glenn Waldron : Pelican Mapping : http://pelicanmapping.com :
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