UTM zones - west edge, overlap, v.mkquads

[Gerald I. Evenden]

>From: Scott Wade <wade at zorro.cecer.army.mil>
>Subject: UTM zones - west edge, overlap, v.mkquads
>
>  Can someone provide a quick lesson on the nature of UTM
>  zones?  I thought there was some overlap between adjacent
>  zones, with low eastings in one zone overlapping with the
>  high eastings of the neighboring zone on the west.  True?

The only match is the northing value for adjacent zone will match
at the seam mid-way between the zones (where longitude evenly
divisible by 6 degrees).

>  Why I ask:  I need a vector layer of USGS quadrangle edges
>  in a location that is on the west edge of zone 12.  If
>  I run v.mkquads with a very low number for the west edge
>  of the current region, v.mkquads fails with this message:
>
>  Zone of the given point (zone: 11) does not match zone of the current window 12
>  Can't go across UTM zones.
>
>  This message is received with any west edge set to less than 218244.
>
>  Oddly, the east side of the region seems to be extensible for quite
>  a distance, with v.mkquads working fine with an east edge
>  of, for example, 1500000.
>
>  Theoretically, doesn't a UTM zone have a west edge of zero?
>  And what's so magical about E218244?
>
>  thanx
>
>  ////\\\\////
>  Scott Wade
>  wade at zorro.cecer.army.mil

This is an endemic problem.

UTM is a fine projection when used withing the constraints of its
definition: large scale mapping in regions that can be contained in
its zone system.  But when attempting to use it outside these
restrictions, all Hell breaks loose.

The most appropriate answer for this problem is to not use UTM, but
this gets into all the details for making an appropriate choice.
Users want something simple when the right answer is not simple,
but there HAS to be something better than UTM.

To Scott: sorry I did not fully answer your questions, but I am
	getting stressed over the over/mis-use of UTM.  If you have
	the flexibility of using something other than UTM and want
	some help, please contact me direct.

Gerald (Jerry) I. Evenden   Internet: gie at charon.er.usgs.gov
voice: (508)563-6766          Postal: P.O. Box 1027
  fax: (508)457-2310                  N.Falmouth, MA 02556-1027