External Evaluation of Road Networks

Internal self-diagnosis and external evaluation of the obtained results are of major importance for the relevance of any automatic system for practical applications. Obviously, this statement is also true for automatic image analysis in photogrammetry and remote sensing. Recently, automatic systems for the extraction of road networks reached a state in which a systematic evaluation of the results seems to be meaningful. This paper deals with the external evaluation of automatic road extraction results by comparison to manually plotted linear road axes used as reference data. The comparison is performed in two steps: (1) Matching of the extracted primitives to the reference network; (2) Calculation of quality measures. Each step depends on the other: the less tolerant is matching, the less exhaustive the extraction is considered to be, but the more accurate it looks. Therefore, matching is an important part of the evaluation process. The quality measures described in this paper comprise measures for the evaluation of the road axes, the network properties, and the crossings. The evaluation methodology is described in detail. Results for the evaluation of simulated as well as real data are presented and discussed. They show the behavior of the quality measures with respect to different deficiencies of the extraction results.