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Show 34 element. We will first review plane surface algorithms similar to those of Bouknight [2], Romney [15] and Watkins [19]. In all of these, the surface representation form of the polygons is effectively algebraic, ie. of the form ax+by+cz+d=O. We will then show how this can be generalized to second order (quadric) algebraic surfaces with an algor ithm similar to those of l'-1ahl [12] and MAGI [11]. Finally, a brief sketch of the general parametric algorithm will be given. Overview To generate the intensity of element we must first know what potentially visible at that spot. a particular picture surfaces, if any, are i.e., which surfaces would appear at that spot in the absence of other surfaces. Then the Z coordinates of the potentially visible surfaces are computed at the X,Y coordinates of the pixel. The particular surface with the closest Z is chosen as the one actually visible. The displayed intensity is computed from the'position in space of the surface fragment and the direction of the vector normal to the surface at that point. All these computations could be performed afresh for each picture element. However the properties of the surface definition function usually make an incremental solution mUch more efficient. For example, for a plane defined by ax+by+cz+d=O, the Z coordinate can be found at any X,Y by the formula |
