An approach to extract watersheds and watercourses, as well as their corresponding valleys and hills, from images with subpixel precision is proposed. The critical points of the terrain are essential as the starting points for the construction of these separatrices. They are extracted efficiently with subpixel precision using an approach based on derivatives of Gaussian filters. The separatrices are extracted by integrating their defining differential equation. Finally, the hills and valleys are constructed by an efficient graph search algorithm.
Examples show the quality of the results that can be achieved with the proposed approach.