Gradual road network simplification with shape and topology preservation.

In this paper, we consider the problem of gradual road network simplification, where given an embedded road network the goal is to compute a fine-grained succession of simplifications with decreasing level-of-detail. This allows to render the network on any desired zoom level or with a user-defined number of segments. Previous work has established that this can be achieved based on a Contraction Hierarchies (CH) data structure. CH was originally developed as a graph preprocessing method to speed up shortest path planning in road networks. However, since it is inherently based on a graph simplification mechanism, it can also serve as a basis for rendering. But the existing method exhibits several shortcomings, for example, topological inconsistencies arise on many simplification levels and the preservation of the shape of routes and the overall network for coarser graph representations is insufficient. This severely impairs the navigability of the map. We significantly improve upon the existing method by modifying the CH construction process as well as the rendering algorithm.