[Xastir] Datum conversions

[Curt Mills]

On Sun, 19 Dec 2004, Gerry Creager n5jxs wrote:

> The Universal Transverse Mercator projection divides the Earth's
> surface, generally, into parcels 6 deg wide, divided at the equator, and
>   typically too distorted to use past some arbitrary point (42 deg N &
> S, but that's what I remember and can't document at this time...).

84N is the max, 80S is the min.  Closer to the poles from either of
those you end up using UPS.  Boy do I remember how hard it is to
find definitive docs on UPS!

Xastir support UTM/UPS fully.  I just used it to determine again
what those limits were.  The 6 degree blocks is mostly correct.
There's some fudging of those sizes in northern Europe and above, so
you have a few 3/9/12 degree blocks.  Some UTM/UPS coordinate
systems use those funny-size blocks, other use regular 6-degree
blocks throughout.  I think the messed-up system is used by NATO and
the U.S. Military, but it's also used by some of the countries that
have land in that region.

That's why we give you a choice between "UTM" and "UTM w/special
zones" in Xastir.

-- 
Curt, WE7U.				archer at eskimo dot com
http://www.eskimo.com/~archer
  Lotto:  A tax on people who are bad at math. - unknown
Windows:  Microsoft's tax on computer illiterates. - WE7U.
The world DOES revolve around me:  I picked the coordinate system!"