As we mentioned before here Course angle and the distance between the two points on loxodrome (rhumb line)., if you are traveling the Earth surface from the point A to the point B maintaining the same course angle, your current path won't be the shortest distance between these points.
To achieve your target with the shortest path you have to correct your course angle so the trajectory of you movement will be close to the great circle (orthodromy), that will be the shortest distance between these two points. The following calculator calculates the distance between two coordinates, the initial course angle, the final course angle and the course angles for the intermediate points. The difference of this calculator from the earlier version Distance calculator is that this one is using quiet precise algorythm, developed by Polish scientis Thaddeus Vincenty. The calculation error is less than 0.5mm.
Firstly, the inverse position computation was solved - the distance between the two points was calculated and the initial and final grid azimuths were found. Then the aquiered distance was divided into an equal number of segments in accordance with a predetermined number of waypoints and for every segment the common survey computation was solved - the coordinates of the next point were found by the given directional angle and the coordinates of the previous point. For this solution the Vincenty's algorythm was used (It's described here Direct and Inverse Solutions of Geodesics on the Ellipsoid with application of nested equations, Survey Review, April 1975)