Shortest distance between two points along the surface of a sphere, known as the great circle or orthodromic distance, can be computed from:

Where r is the radius of the sphere and the central angle (Δσ) is computed from the Cartesian coordinate of the two points in radians. Here n₁ and n₂ are the normals to the ellipsoid at the two positions. The above equations can also be computed based on longitudes and latitudes of the points.

However, the shortest distance in general can be computed by algorithms such as Dijkstra, which computes the shortest distance on graphs. In this case the image is represented as a graph in which the nodes refer to the pixels and the weight of edges is defined based on the connectivity of the points and their distance.