Priority pixel queue algorithm for geodesic distance transforms

The sequential mask operations for calculating distance transforms may have to be iterated several times in the case of geodesic distances. This article presents an efficient propagation algorithm for the Distance Transform on Curved Space (DTOCS). It is based on a best-first pixel queue, and is applicable also for other gray-level distance transforms. It eliminates repetition of local distance calculations, and performs in near-linear time. A nearest neighbor transform based on distances along the surface, and a propagation direction image for tracing the shortest paths, can be produced simultaneously with the distance map.