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Show CHAPTER IV ILLUMINATION MODEL IV. 1 Curvature of the surface at each vertex. For point any . a mathematically can described model, the curvature of be determined surface at that point. In the The curvature of a surface at exactly by solving the equation which determines the of case approximation of its curvature its can described polygonally a model, only an be obtained. polygonally described surface is the from obtained orientation and magnitude of the normal to the surface at that point. The determination of the approximating a surface surface at each vertex. method used used techniques 1. 2. to products graph approximate in Figure vertex each of the polygons computation of the normal to the 4.1 shows characterization of a the normal to the surface at a vertex. Two each commonly are: Approximation the at is then reduced to the The Approximation by In curvature averaging from the the edges which terminate first case, the normal to of all the of normals a adjacent pairs of edges diagram of Figure 4.2., the normal to the polygon of the the surrounding polygons. at the vertex. the is polygon. polygon PI, P2, ... , sum of the In the example P6 is: cross on the |
