[GRASS5] Lat conventions - r.proj

[Alessandro Frigeri]

Hello,

I've found different definitions of latitude on different books, it
seems to me that the problem is not the term 'latitude' but the extra
term geocentric or geodetic that often is not specified in books and
various documents.

So i summarize what I found as follows: 
-geocentric latitude is the angle beetween the equatorial plane and a
vector from the center of the ellipse and the point on the surface. 
-geodetic latitude is the angle beetween the normal to the surface at a
point and the equatorial plane. 

For a sphere two equal latitudes point to the same place but not in the
case of ellipsoid.

Since at the moment I'm studying reference systems in planets, I wonder
what lat convention is used in a GRASS lat/lon location? Is there the
chance to pass beetween the two systems (m.gc2ll and m.ll2gc and some
simple trigonometry make the trick) in one passage? 

I read on manpage that r.proj does't convert datum a part NAD27/83.  Is
it still true or are there news about it in CVS?

Stupid questions? don't hesitate to let me know!


Cheers

Alessandro Frigeri



-- 
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Alessandro Frigeri
PhD Student in Structural Geology
		      Earth Science Department
                      University of Perugia
                      Perugia, ITALY
Radio Amateur Callsign: IK0YUP 
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