Implementation of Donald elliptic projection for VH coordinates and calculation of air mileage

Geographic coordinate system (represented in latitude and longitude) considers earth as a perfect sphere. But in fact its shape is slightly elliptical. This assumption puts limitations on the accuracy of distance calculated between any two points on earth. While this small error is neglected in most distance calculator algorithms, applications demanding perfect distance between any two points need alternative way to compute that. One approach to solve this problem is Jay K. Donald's elliptic projection. In this paper we briefly describe the back-ground of elliptical projection and presents an implementation of the algorithm that yields geographical coordinates from given vertical-horizontal pair. The vertical and horizontal coordinates can be used to calculate near perfect air mileage between two points. Experiments on some sample real addresses show that the calculated aerial distances are more accurate than the ones calculated by methods that do not consider earth's oblate spheroid shape.