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Abstract: "This paper reports progress toward the development of a representation of significant surface changes in dense depth maps. We call the representation the Surface Primal Sketch by analogy with representations of intensity changes, image structure, and changes in curvature of planar curves. We describe an implemented program that detects, localizes, and symbolically describes: steps, where the surface height function is discontinuous; roofs, where the surface but the surface normal is discontinuous; smooth joints, where the surface normal is continuous but a principal curvature is discontinuous and changes sign; and shoulders, which consist of two roofs and and correspond to a step viewed obliquely. We illustrate the performance of the program on range maps of objects of varying complexity."

Abstract: "This paper presents a new approach to the computation of stable grasps of curved two-dimensional objects. We consider the case of a hand equipped with two hard fingers and assume point contact with friction. Objects are modelled by parametric curves, and force-closure grasps are characterized by systems of polynomial constraints in the parameters of these curves. All configuration space regions satisfying these constraints are found by a numerical cell decomposition algorithm based on curve tracing and continuation techniques. Maximal object segments where fingers can be positioned independently are found by optimization within the grasp regions. The approach has been implemented and examples are presented."

Computing surface and/or object intersections is a cornerstone of many algorithms in Geometric Modelling and Computer Graphic, for example Set Operations between solids, or surfaces Ray Casting display. This document presents an object centered, information preserving, hierarchical representation for polyhedra called Prism Tree. The author uses the representation to decompose the intersection algorithms into two steps: the localization of intersections, and their processing. When dealing with polyhedra with many faces (typically more than one thousand), the first step is by far the most expensive. The Prism Tree structure is used to compute efficiently this localization step. A preliminary implementation of the Set Operations and Ray Casting algorithms has been constructed. (Author).

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