Tham khảo tài liệu 'dynamic vision for perception and control of motion - ernst d. dickmanns part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Objects 45 model both with respect to shape and to motion is not given but has to be inferred from the visual appearance in the image sequence. This makes the use of complex shape models with a large number of tesselated surface elements . triangles obsolete instead simple encasing shapes like rectangular boxes cylinders poly-hedra or convex hulls are preferred. Deviations from these idealized shapes such as rounded edges or corners are summarized in fuzzy symbolic statements like rounded and are taken into account by avoiding measurement of features in these regions. Shape and Feature Description With respect to shape objects and subjects are treated in the same fashion. Only rigid objects and objects consisting of several rigid parts linked by joints are treated here for elastic and plastic modeling see . Metaxas Terzepoulos 1993 . Since objects may be seen at different distances the appearance in the image may vary considerably in size. At large distances the 3-D shape of the object usually is of no importance to the observer and the cross section seen contains most of the information for tracking. However this cross section may depend on the angular aspect conditions therefore both coarse-to-fine and aspect-dependent modeling of shape is necessary for efficient dynamic vision. This will be discussed for simple rods and for the task of perceiving road vehicles as they appear in normal road traffic. Rods An idealized rod like a geometric line is an object with an extension in just one direction the cross section is small compared to its length ideally zero. To exist in the real 3-D world there has to be matter in the second and third dimensions. The simplest shapes for the cross section in these dimensions are circles yielding a thin cylinder for a constant radius along the main axis and rectangles with the square as a special case. Arbitrary cross sections and arbitrary changes along the main axis yield generalized cylinders discussed in
