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Chris W Skelly
gewcs at jcu.edu.au
Thu Jul 8 01:45:30 EDT 1993
On Wed, 7 Jul 1993, Net.Noise owner wrote:
>
> In <9307070737.AA12583 at bushland.ecn.purdue.edu> mccauley at ecn.purdue.edu (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 s.surf.krig 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. s.surf.krig is
written using spherical geometry.
If this response is even close give me a buzz, if not SORRY.
chris
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