Re: Confused by DATUM's

On Sat, 25 Nov 2006 15:35:54 -0600, Richard Owlett
<rowlett@xxxxxxxxxxxxx> wrote:

Sam Wormley wrote:

Richard Owlett wrote:

I can "see" rectil-linear (sp?) systems such as UTM having a
dependence on presumed shape of earth.

Why/how would this influence a readout in
latitude/longitude/elevation(assumed to be distance from earth's
center of gravity).

What SIMPLE thing am I missing?

TIA


There are a number of ellipsoids that attempt to be a good
fit for a portion of the earth.
http://www.colorado.edu/geography/gcraft/notes/datum/edlist.html

Upon which are built many different datums (ellipsoid) for reference
point. Universal Transverse Mercator (UTM) coordinates define two
dimensional, horizontal, positions--in a localized region.

http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html#utm

-Sam Wormley
http://edu-observatory.org/maps/utm.html


I looked at them.
What questions should I be asking ?

I think I'm missing something fundamental.

You can try my explanation of Datums at
http://www.gpsu.co.uk/datums.html

This might help to explain it better.

Alan Murphy. (author GPS Utility)
.

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