外文翻譯--實現(xiàn)三維異常照(編輯修改稿)
2025-02-04 08:13 本頁面
【文章內(nèi)容簡介】 edron. The output of the system can be used as toy material from which children construct the impossible objects. We review the basic results in pictureinterpretation theory in Section 2, and characterize the class of anom alous pictures that are correct projections of polyhedra, inSection 3. In Section 4, we describe the interactive sys tem for generating unfolded surfaces of such polyhedra, and show some examples of objects generated by the system. 2. REVIEW OF PICTUREINTERPRETATION THEORY . Realizability problem Suppose that the (x, y, z) coordinate system is fixed in a threedimensional space. Let D be a line drawing fixed in the plane z=l. We say that D is realizable if D is the projection of some polyhedron in the threedimensional space. We are interested in judging whether D is realiz able. As shown in Fig. 1, let us assume that the polyhedron is projected on to the picture plane z= 1 by the perspective projection with the center of projection at the origin (0, 0, 0). This assumption does not restrict the problem because whether D is realizable or not does not depend on whether the projection is orthographic, oblique or per spective.(17) . HuffmanClowes labeling scheme The first step for the interpretation of the line drawing D is to find a reasonable number of candidates of the spatial structure which the picture D may represent. For this purpose, the HuffmanClowes labeling scheme is employed. (1,5) We use the terms vertices, edges and faces to represent geometric elements belonging to a polyhedron, and use the terms junctions, line segments (lines for short) and regions, respectively, to represent their images in the line drawing. An edge is said to be convex if the associated two side faces form a ridge along this edge, and concave if they form a valley. A line is called a concave line if it is the image of a concave edge。 we assign the label to this line. A line is called a convex line if it is the image of a convex edge and if the associated side faces are both visible。 we assign the label + to this line. A line is called an occluding line if it is the image of a convex edge and if one of the associated side faces is invisible。 we assign the arrow to this line in such a way that both of the associated side faces are to the right of the arrow. Huffman (5) and Clowes (1) constructed the plete list of possible binations of labels around junctions。 this list is now called a junction dictionary. They found candidates of the spatial structure represented by the line drawing D by assigning labels to lines in such a way that the binations of labels at junctions are consistent with the junctio
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