Proc. IEEE Workshop on Qualitative Vision, 1994.
We address the problem of computing the exact aspect graph of a polyhedral object observed by an orthographic camera with finite resolution, such that two image points separated by a distance smaller than a preset threshold cannot be resolved. Under this model, views that would be different under normal orthographic projection may become equivalent, while "accidental" views may occur over finite areas of the view space. We present a catalogue of visual events for polyhedral objects and give an algorithm for computing the aspect graph and enumerating all qualitatively different aspects. The algorithm has been fully implemented and results are presented.