Notation
Define the following notation:
| a | length of semi-major axis of the ellipsoid (radius at equator); | (6378137.0 metres in WGS-84) |
| ƒ | flattening of the ellipsoid; | (1/298.257223563 in WGS-84) |
| b = (1 - ƒ) a | length of semi-minor axis of the ellipsoid (radius at the poles); | |
| φ1, φ2 | latitude of the points; | |
| U1 = arctan, U2 = arctan |
reduced latitude (latitude on the auxiliary sphere) | |
| L = L2 - L1 | difference in longitude of two points; | |
| λ1, λ2 | longitude of the points on the auxiliary sphere; | |
| α1, α2 | forward azimuths at the points; | |
| α | azimuth at the equator; | |
| s | ellipsoidal distance between the two points; | |
| σ | arc length between points on the auxiliary sphere; |
Read more about this topic: Vincenty's Formulae