Alternative routes in complex environments


Due to the immense dissemination of low-cost GPS receivers built into mobile devices, an impressive use of location-based services has been achieved in recent years. A popular application is navigation in road networks in conjunction with the presentation of alternative routes that allows users a choice according to their own preferences or experiences. Route finding in complex environments differs from that in road networks mainly due to the fact that a user can move almost in all directions. Examples include pedestrians in airports, hospitals, exhibition halls, or parks, mobile robots in industrial facilities or warehouses, as well as non-player characters in computer games. In these scenarios the provision of alternative routes is useful, too, for example, to enable personalized navigation, to avoid jams proactively, or to carry out tactical movements. This thesis presents approaches which deal with the topic of alternative routes in complex environments at different thematic levels. This includes the calculation of alternative routes in open space, the comparison of geospatial trajectories, and the identification of structures in buildings. First, alternative routes in complex environments are defined using the topological concept of homotopy, so that two routes can be considered alternative if they pass obstacles differently. For this purpose an effcient approximation of the homotopy test is presented together with the implementation of two algorithms for the calculation of such routes. Subsequently a structured presentation of existing quality metrics for alternative routes and alternative graphs in road networks takes place, whereupon the transferability of these approaches into complex environments is discussed. Second, approaches for the direct comparison of routes are presented. On the one hand, a scoring of routes is suggested based on the assumption that routes, which often lie on a shortest paths, are also often traversed. On the other hand, a system is presented that allows the calculation of archetypal routes by extracting the most extreme instances from a set of routes. Corresponding to this, the archetypal distance is defined, with which routes can be compared not only geometrically but in a multi-dimensional feature space. Third, the quantitative analysis of the visual perception of space is incorporated into the context of alternative routes. Based on the idea of so-called Isovists, a user’s local environment is approximated in order to calculate alternative routes, to annotate them, and to determine structures in buildings. In summary, the contributions of this thesis can be understood in their entirety as a toolbox which can be used by other location-based services.