“…[1,7,11,15, 23], they do not lend themselves to the description of curving segments of contour as units unto themselves, as seen in figure 2. For this reason, workers in geometric modeling as well as computer vision have turned to more complex parametric models, including circular arcs [6,10,16, 24J, more general conics [5, 271, and splines [12,14,19,25]. In general, the analytic form selected for describing contour segments should be matched to the domain-dependent processes that generate the contours; for example, if all images for a given task are oblique views of circular objects, then elliptical models are appropriate for describing the contours which will be found in the resulting images.…”