Timz From United States of America, joined Sep 1999, 6644 posts, RR: 7 Reply 1, posted (9 years 5 months 5 days 3 hours ago) and read 2163 times:
"GCM uses gnomonic projection for calculation itself"?
Dunno what this means. It calculates the geodesic distance, probably using Vincenty's formulas or something similar. It uses the wrong spheroid, so it can be off by a fraction of a kilometer, but the formulas are probably correct.