[Proj] Accurate algorithm for geodesic calculations

Karney, Charles F. ckarney at Sarnoff.com
Mon Mar 2 06:15:25 EST 2009

> I am assuming that this calculates the elliptic path (on some
> reference ellipsoid) between any 2 points, without elevation? Yes?

Correct.  Elevation doesn't come into this treatment.  However the
geodesic path is not an ellipse -- in general the geodesic for an ellipsoid
doesn't lie in a plane.

> Can somebody post same for a direct "laser line" between any two points
> and with elevation on both ends. This must be a more common problem
> when doing shorter ground measurements.

The simple way of doing this is to convert both geodetic points to
geocentric and use Pythagoras.  I've used this method to obtain range
maps for a terrain from a particular viewpoint.

Charles Karney <ckarney at sarnoff.com>
Sarnoff Corporation, Princeton, NJ 08543-5300

URL: http://charles.karney.info
Tel: +1 609 734 2312
Fax: +1 609 734 2662

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