projection

[Gerald I. Evenden]

>From: "ROMAN ANTONI KAMINSKI" <TSS at mwod.sggw.waw.pl>
>Sender: grass-lists-owner at moon.cecer.army.mil
>To: mskc at io.com (Casey Claiborne), grassu-list at max.cecer.army.mil
>Date:          Sat, 19 Aug 1995 13:47:18 MET-1
>Subject:       Re: projection
>
>>From 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, 1989
>
>And 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 at charon.er.usgs.gov
voice: (508)563-6766          Postal: P.O. Box 1027
  fax: (508)457-2310                  N.Falmouth, MA 02556-1027