Distance and bearing calculation

This program written for the 18F452 takes the latitude and longitude of two stations and calculates the distance between them and the bearing of the remote station from the home station.

It takes into account the ellipsoid nature of the earth with adjustments for the central angle effect on latitude and the distance due to the non spherical shape.

This solution is considerably longer than the simple application of spherical geometry but it does result in at least double the accuracy. In some test runs it calculates distance differences of up to 20km from the simple approach.

There is a real limit on accuracy due to local terrain and as its most used application is for calculating the distance of radio paths the vagaries of propogation also affect the actual path. The method of measuring latitude and longitude must be the same for both sites (same map or GPS) .

The author recognises the work done by the authors of a book "Morris, Amateur Radio Software published by RSGB" for the main routine.

The software was tested in the demo version of ISIS provide in the PDS package.

John
VK5DJ