Gerald I. Evenden
gevenden at capecod.net
Sun Apr 2 11:53:48 EDT 2000
I have thought about MGRS a couple of times but felt it represented
a zone or regional designation rather than a point and thus a little
more difficult to determine a rigorous determination.
Regarding "automatic" UTM by only specifying longitude, there is
a technical problem: UTM zones allow a half degree overlap (actually
3.5 degrees wide) so geographic coordinates laying in this region
are ambiguous as to which zone to apply. Secondly, this ambiguity
always exists for those points on the even 6 degrees.
One can also specify the central meridian for UTM and PROJ.4 will
automatically adjust it to the proper zone CM. BUT, if the specified
CM is on an even 6 degrees the determination may toggle to either
CM. Remember, CMs are on all 6xN+3 degree meridians.
Lastly, even if the longitude could be used as a CM determinator,
the control stucture for the projection would have to be
intialized for *each* lat/lon determined. That is, open and closed
for each point computed.
As for getting the zone number used out of an opened control
structure... Hmmm. First, I don't recall if the zone number is preserved
in the structure and secondly, projection specific contents of the structure
only defined in the UTM/tmerc code and may not globally available.
I *really* don't think this is a good idea.
Oh yes! Some zones in the Scandinavian region have funky limits
and simplistic determination from longitude cannot be used.
Hey, if elephants could fly.
Jerry Evenden and the low riders: Katie and Daisy-Mae
gevenden at capecod.net http://www.capecod.net/~gevenden
From: Rick Brownrigg <brownrig at erg.sri.com>
To: osrs-proj at remotesensing.org <osrs-proj at remotesensing.org>
Date: Sunday, April 02, 2000 11:10 AM
Subject: [OSRS-PROJ] MGRS?
>I'd like to inquire if there's any interest in support for MGRS in the
>Proj library -- anybody else use this?
>There's support in other places, but I find it awkward to use Proj for
>some purposes, another library for MGRS, etc. I can certainly take the
>lead in coding/testing if thats what it takes. I have a number of
>reference sites, however I'd appreciate any pointers others may have as
>Note, that it unfortunately requires additional interfaces into the
>library, as the MGRS coordinate is a string (typically 15 characters),
>not a pair of doubles.
>BTW: on a related topic, I've found the UTM support awkward to use.
>Ideally, I'd like to plug in a Long/Lat pair, and get back UTM with the
>"proper" zone number. Currently, one must *know* the zone and use that
>as a projection parameter. Both behaviors are useful. This would also
>require additional interface mods. Comments?
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