MATCHING OF ROAD DATA OF GREATLY DIFFERENT SCALES AND
CONSTRUCTION OF A MULTIPLE REPRESENTATION DATABASE
P. Luescher, D. Burghardt, R. Weibel
University of Zurich, Department of Geography, Zurich,
Switzerland
luescher@geo.unizh.ch
Multiple representation databases (MRDB)
contain several geographic datasets covering the same area. In an MRDB, the
objects within the different datasets that model the same real-world phenomenon
(also termed homologous objects) are linked with each other. Thus MRDB allow
better consistency control between integrated datasets and cheaper updating by
propagating updates of one dataset automatically into all other datasets.
Equally important is the potential for new visualisation methods, for example
by allowing a seamless zoom in real-time between two interlinked scale levels.
There exists already a large quantity of
datasets and these have to be integrated into MRDB as well. Since manual
integration would often be too tedious and time-consuming, automatic matching
techniques that find homologous objects and create the links between them have
to be developed. While existent matching processes have been designed for
datasets that are of the same or at least similar scales, the goal of our work
was the development of such a matching technique for road data of greatly
different scales, e.g. 1:25.000 and 1:200.000.
Several challenges arise. Firstly, the
conceptualisation of real-world objects varies in different scale levels. For
instance, roundabouts collapse to single points in smaller scales; highways are
just portrayed by their centreline, while in larger scales usually single lanes
are modelled. Secondly the larger scale road network is much denser, and thus
many short road segments of the larger scale have to be assigned to one single
road of the smaller scale. Thirdly, because smaller scale roads are strongly
generalised, geometry of homologous objects may differ considerably.
The matching method developed by us works in
three stages: An initial filtering of smaller scale features generates probable
matching pairs; then links between crossroads are created; finally the
crossroads assignments are converted into road assignments. The filter step
could be enhanced significantly by employment of an algorithm termed closest path, a shortest path algorithm
that minimizes the Hausdorff distance between a reference road of the smaller
scale and the set of possible matching candidates of the larger scale. In the
matching stage, match precipitation by means of a line tracing module is used.
The matching algorithm has been evaluated with
road data at the scales of 1:25.000 and 1:200.000, respectively. A comparison
of the results to manually matched reference data showed that the method worked
very well in areas with low to medium density of settlements, but had some
deficiencies in complex urban zones. Therefore we propose to add an initial
classification into rural and urban areas, and to adapt the algorithm
parameters accordingly.