From:kls@ohare.Chicago.COM (Karl Swartz)Organization:Chicago Software Works, Menlo Park, CaliforniaDate:04 Oct 95 22:57:26References:1Followups:1 2

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>I wonder if anyone can provide me with the formulae to calculate great >circle course and distance given the latitude and longitude of the >departure point and destination. Distance itself is pretty easy. Given latitude and longitude in radians, compute the angle (theta) between the initial and destination longitudes and normalize it to the range -PI .. PI. The distance as an angle is then acos( sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(theta) ) Multiply that by the radius of the earth (i.e., 6371.2 kilometers) to get a reasonable approximation of the great circle distance. Plotting the course is considerably more work. You might want to look at the 'geod' program included with the PROJ.4 mapping program, which can be picked up via anonymous ftp from charon.er.usgs.gov. -- Karl Swartz |Home kls@chicago.com |Work kls@slac.stanford.edu |WWW http://www.chicago.com/~kls/ Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills