Steve Baker (sbaker++at++link.com)
Fri, 24 Oct 1997 14:00:18 -0500 (CDT)
> What gives?????
>
> I thought this place was for help??
I agree. If you can't say something useful, don't say anything. That
goues double for mailing lists with >600 people on them.
As I said before, check out:
http://www.utexas.edu/depts/grg/gcraft/notes/coordsys/coordsys.html
That web site contains more information than you could possibly need
to know about map projections. It also has links to all sorts of other
resources.
The summary version is:
* Are you going from Lat/Long/Altitude to a *FLAT* earth representation
of to a *CURVED* earth representation? This makes a big difference
to the answer.
IF FLAT EARTH THEN:
* Realise that you can only get an approximation to reality, and
you have to choose which kinds of errors to accept. The two
most frequently used algorithms are Lambert and Transverse Mercator.
Neither is better in an absolute sense - one minimises the error
in distances between places as measured on the flat surface as
compared to on the true earth, the other minimises angular errors.
I forget which is which.
IF CURVED EARTH THEN:
* Can you simply approximate the earth as a sphere?
IF SO THEN
* A couple of sin/cos calls and you are done.
ELSE
* The 'official' standard for the shape of the earth was
defined in 1984 and is called 'WGS-84'. It is a description
of a squashed ellipsoid.
Steve Baker 817-619-8776 (Vox/Vox-Mail)
Hughes Training Inc. 817-619-4028 (Fax)
2200 Arlington Downs Road SBaker++at++link.com (eMail)
Arlington, Texas. TX 76005-6171 SJBaker1++at++airmail.net (Personal eMail)
http://www.hti.com http://web2.airmail.net/sjbaker1 (personal)
** Beware of Geeks bearing GIF's. **
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