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Chris W Skelly gewcs at
Thu Jul 8 01:45:30 EDT 1993

On Wed, 7 Jul 1993, Net.Noise owner wrote:
> In <9307070737.AA12583 at> mccauley at (Darrell McCauley) writes:
> >Trying to make my programs more lat-long friendly...
> >
> >  d = G_distance (x1, y1, x2, y2);
> >
> >  angle = 180.0 / 3.14159 
> >        * acos ((G_distance(x1,y1,x2,y1)+G_distance(x1,y2,x2,y2)) /2.0 
> >        / d);
> What I think you want is an azimuth calculation and I'm sure this
> isn't the right way to do it. There is no formula in GRASS presently
> neither for spheres or ellipsoids. Does someone have a reference for
> this calculation so it can be coded and added to the GRASS library?
> >Is this correct approach? Is there a library function that I am
> >missing which would do what I want?

I wonder if I am going to muddle this more. :-()

I do believe that when I was writing the code that
G_distance did indeed call a function that specified a sphere or
elleipse. You are looking for a spherical or elliptical geometric
function to calculate the distance over a curved surface arn't
you?  I am sure these routines are already in GRASS, start looking
in G_distance and follow its calls, I ended up not using it
because I couldn't get it to work properly. is
written using spherical geometry.

If this response is even close give me a buzz, if not SORRY.


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