Generation and generalization of safe depth-contours for hydrographic charts using a surface-based approach

Depth-contours are an essential part of any hydrographic chart—a map of a waterbody intended for safe ship navigation. Traditionally these were manually drawn by skilled hydrographers from a limited set of surveyed depth measurements. Nowadays this process of map making is shifted towards the digital domain, not in the last place because of the sheer size of the point clouds that result from modern surveying techniques such as Multi Beam Echo Sounding (MBES) (see Figure 1a). This is no trivial task, since the the produced depth-contours need to comply with the four hydrographic generalization constraints of safety, legibility (smoothness), topology and waterbody morphology. The challenge is to solve the generalization problem for these four constraints.