Eric Hirschorn (eric123++at++airmail.net)
Fri, 24 Oct 1997 21:30:53 -0500
The UTM transformations are pretty involved, especially
when dealing with an ellipsoidal Earth model. It is possible to
skip over the derivations and use canned routines, and still
have a basic understanding of what is going on. But I
understand if you are one of the few who need to derive the
results - although I am not one of those few, I am still interested in
the topic. On the other hand, if you just need public domain
software w/o the derivations I can point you to a source:
http://everest.hunter.cuny.edu/mp/software.html
In the spherical Earth case I'm sure the equations simplify
a bit, but I'm not sure if you are on the right track or not
on the "Great Circle". Your equation for Y, for example, reduces
to Y/6378137=lat, which I don't think can be better than a rough
approximation for small lat. Your expression for X looks pretty
suspicious also, but right now just in the intuitive sense. What
lat,lon conditions do you think the "Great Circle" correspond to?
More basically, are you trying to project a sphere onto a transverse
cylinder, which is part of the meaning of UTM?
I am interested in the topic, so feel free to send me your
derivations via fax: (817) 619-4028. As you see, your alleged
trolling activities were entirely successful.
Eric
Garrett Williams wrote:
>
>[...]
> any way From what I have found out so far I wish to go from lat/long's
> to utm's.. I am getting close with the "GreatCircle" but my X value is
> off a bit...
>
> here is what I have so far...
> X=6378137*acos( (sin(lat) * sin(lat)) + (lat) * cos(lat) * cos(-long))
> );
> Y=6378137*acos( (sin(0) * sin(lat)) + (cos(0) * cos(lat) * cos(0)) );
>
>
> Wacha think
--
Eric S. Hirschorn
eric123++at++airmail.net
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