Instead of Vincenty's, there is a very nice Meeus method for great circle distance, which has virtually identical accuracy and no loop inside; http://www.abeced

Instead of Vincenty's, there is a very nice Meeus method for great circle distance, which has virtually identical accuracy and no loop inside; http://www.abecedarical.com/zenosamples/zs_great_circle_route.html http://www.abecedarical.com/zenosamples/zs_great_circle_rout...