Re: Calculating a Distance on the Surface of the Earth

O.B. wrote:
I've managed to summarize the problem I'm trying to solve in the PDF
below. Basically, I have a point on the earth's surface at a given
latitude and longitude. If I moved 200km away from this point to the
East, I'd actually be above the surface of the earth due to the
curvature of the earth. If at the point, I were to drop straight down
to the surface of the earth, I'd like to know the distance between
this new point on the earth and the original point. I'd like to
repeat this calculation with heading 200km to the North. Help?

http://www.dafunks.com/misc/EllipseProblem.pdf

If I understand you correctly, you want a "circle" a distance, D, from a point, P, given as lat and lon. By "circle", I mean a series of points that are distance, D, on the ellipsoid from P.

I have implemented both Sodano's direct and inverse methods in APL2. It is not trivial to get to the full accuracy as described in the appendices of Sodano's paper but I did and according to my comparisons with the best data I could find, my functions are good for distances of a few meters up to several thousand Kilometers. If you have access to APL2, I would be happy to send you a *.ATF file of the functions. Using these functions it is trivial to find the coordinates of one or more points a given ellipsoidal distance from a point P.

I chose to use Sodano rather than Vicenty since Sodano's algorithms are not iterative and this is generally faster, more accurate and more versatile in APL.

Ted
.

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