English: A geodesic on an ellipsoid of revolution. N is the north pole. A is a point at latitude φ₁; B is the point at latitude φ₂ which is λ₁₂ east of A. AB is the geodesic from A to B. E is the point at which the geodesic crosses the equator, EFH, in the northward direction. NE, NAF, and NBH are meridians. The azimuths of the geodesic at E, A, and B are α₀, α₁, α₂, respectively. The direct and inverse geodesic problems solve the triangle problem NAB given an angle, α₁ for the direct problem and λ₁₂ for the inverse problem, and its two adjacent sides.