[Gdal-dev] UTM question

[Curt, WE7U]

On Tue, 29 Jun 2004, Clay, Bruce wrote:

> Is there anything in the GDAL package that can given 2 points in either
> geocentric or geodetic coordinates determine the distance between the 2
> points in x and y values?  I realize that UTM is in meters and within a
> given zone all I have to do is subtract.  For some reason I am not
> grasping what has to be done to get an accurate measurement across UTM
> zones.  I like the idea of using the UTM system because it is in meters
> which can easily be scaled in a scene but I can't find anything on the
> web to guide me through what seem like it should be an easy step.

It's not an easy step.  Because of the way UTM zones are defined.
The relationship between points in nearby zones is not a simple one.
Your best bet is to convert to lat/long coordinates, compute the
distance using great-circle coordinates.


> I am working on a 3D visualization package that will be given a stream
> of WGS84 based geocentric coordinates and I need to update the position
> of objects in the scene.  Since the scene is a small area with its own
> sense of altitude (or elevation data) I am treating it like a flat earth
> view and disregarding tilt of the patch to the global reference frame.

I work on a 2D program that can plot moving/stationary objects, and
we can switch between MGRS, UTM, and multiple lat/long
representations for the positions.  Also be aware that there are
some special UTM zones as well, which don't correspond to the
standard zone boundaries.  These are in the Europe area and north.
Our application can switch between the standard zones and these
special zones.

Another note about UTM:  The military actually allows using eastings
that bleed over into the next zone, for such activities as
targeting.  I don't recall off-hand how far into the next zone they
allow this sort of usage.

--
Curt, WE7U			         http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
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