Abstract
An isochrone in a spatial network is the minimal, possibly disconnected subgraph that covers all locations from where a query point is reachable within a given time span and by a given arrival time [5]. A novel approach for computing isochrones in multimodal spatial networks is presented in this paper. The basic idea of this incremental calculation is to reuse already computed isochrones when a new request with the same query point is sent, but with different duration. Some of the major challenges of the new calculation attempt are described and solutions to the most problematic ones are outlined on basis of the already established MINE and MINEX algorithms. The development of the incremental calculation is done by using six different cases of computation. Three of them apply to the MINEX algorithm, which uses a vertex expiration mechanism, and three cases to MINE without vertex expiration. Possible evaluations are also suggested to ensure the correctness of the incremental calculation. In the end some further tasks for future research are outlined. Categories and Subject Descriptors H.2.8 [Database Applications]: Spatial databases and GIS General Terms Algorithms.