Generating an aspect graph by set operations on sets of viewpoints

Recognizing 3-D objects from 2-D images using an aspect graph approach is considered. The authors describe an algorithm for creating aspect graphs for general polyhedral objects, using a closed space centered at the origin of an object as a viewing space. They divide the viewing space into sets of viewpoints according to differences of aspects. An aspect graph is constructed by set operations on sets of viewpoints. The set operations are executed by substituting solid polyhedra for the sets of viewpoints. The algorithm enables the authors to classify aspects of a general polyhedral object under perspective projection, to solve the problem of occlusion caused when an object has nonconvex parts, and to construct aspect graphs automatically