From: "ROMAN ANTONI KAMINSKI" <TSS@mwod.sggw.waw.pl>
Sender: grass-lists-owner@moon.cecer.army.mil
To: mskc@io.com (Casey Claiborne), grassu-list@max.cecer.army.mil
Date: Sat, 19 Aug 1995 13:47:18 MET-1
Subject: Re: projectionFrom g.help
A map coordinate system is either a geographic system
(like UTH or latitude/longitude) or an arbitraly coordinate system
used to reference the locations of objects in a two-dimensional
space.
The geographic system refers to the location on the Earth, not on the
map. Geographic coordinates can often be determined from a map if
the graticule is plotted. But referring to geographic coordinates
as a map coordinate is misleading.
BTW, what is UTH?
A map projection describes the manner in which the spherical
surface of the earth is represented on a two-dimensional surface.
What about the ellipsoid?
It attempts to minimize distortionin area,shape,distance and
direction.
No map projection does all of the above. Select one of the criteria
and a projection may used that does minimize that feature at the
expense of the others.
See also the reference
"Map Projections - A Working Manual " ,Snyder, 1989And my private view.
Projections are used eg for UTH .
Again, what is UTH?
For small area are not needed.
Not true.
I'm a civil engineer and about map projections I learned
50 years ago.
Very little has changed in 50 years. Only item of significance
it the ease of computing a projection.
Now I get the projection from the sample problem.
Later the user from Geography Department will know what
projection to use.BRGRDS Romek
Gerald (Jerry) I. Evenden Internet: gie@charon.er.usgs.gov
voice: (508)563-6766 Postal: P.O. Box 1027
fax: (508)457-2310 N.Falmouth, MA 02556-1027