| 109 | 109 | The medial axis, sometimes also called topological skeleton, is a line version of a polygon where all points on the lines are equidistant to the polygon's boundaries. The medial axis can be used to extract the center line of a polygon, useful e.g. to convert a river represented as a polygon to a line, but also for characterising a polygon's shape, e.g. for object-based classification of images. While the theory for extracting a medial axis is well known, actual implementations often use an approximation instead of the exact medial axis. Extracting the exact medial axis poses problems with regard to floating point accuracy around concave vertices where the medial axis has the form of a parabola. A collection of algorithms exist to define parabola equations around concave vertices, intersect parabolas, and approximate parabolas with straight line segments. A working implementation is not yet available for GRASS. |
