外文翻譯--實現(xiàn)三維異常照-在線瀏覽
2025-02-25 08:13本頁面
【正文】 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 an occluding line if it is the image of a convex edge and if one of the associated side faces is invisible。 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 junction dictionary. Figure 2 shows an example of the consistent labeling. Obviously, this picture does not represent a polyhedron correctly. As shown in this example, a line drawing with a consistent labeling does not necessarily represent a poly hedron correctly. The existence of a consistent labeling is a necessary (but not sufficient) condition for a line drawing to represent a polyhedron. The junction dictionary was generalized for pictures of papermade objects (8) and for pictures with hidden lines. ~3) . Realizable pictures Suppose that the line drawing D has a consistent labeling. We want to judge whether the labeling is a correct interpretation of D. 3. REALIZABLE ANOMALOUS PICTURES The pictures that are traditionally classified as anom alous pictures are not necessarily unrealizable. Some of the anomalous pictures are realizable. (15) Examples of such pictures are shown in Fig. 5. Those pictures are mainly posed of three groups of mutually parallel lines, and wh
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