49 50 Ver6.09.hp Geodesic distance & Earth Euclidean distance calculator, bearing

[Jim Horn]

Wow, Gil, nice work! Back in the early 1980s I needed to compute the great-circle distances involved in the CAFE250 and CAFE400 air races in California. Fortunately, the RAND report (Calculator Programs for Staff Officers) included a Vincenti algorithm program for the then-new HP-67 which I adopted to the HP-41C. I added correction for each waypoint's altitude as well, assuming a constant rate of climb or descent by scaling the distance with a ratio of mid-segment earth radius at altitude to earth radius. A secondary addition of the increase due to the slope itself was made as well. Probably not as accurate as your algorithms but it was fun to do. And it allowed us to modify the race course over the years and get consistent results.

I'll have to bookmark this and both try it on my much-used HP 50g and perhaps port it to my more recent Prime. Should be fun!

Thank you for all the good work!