E1AR0002@SMUVM1.BITNET (Leff, Southern Methodist University) (05/31/87)
[...] Here are some references on converting from 2-D views to constructive solid geometry references. The difficulty is that simply going from three views along orthogonal axis to a 3-D physical description of the problem is ambiguous. That is true, even in the presence of the "hidden line" information that would not be available from a camera. In fact, for a given wire-frame (set of edges of the object), there are many possible corresponding solid objects. %A H. Yoshiura %A Kikuo Fujimura %A T. L. Kunii %T Top-Down Construction of 3-D Mechanical Object Shapes from Engineering Drawings %J COMPUTER %D December 1984 %P 32-40 %K AIME %W 14D %A M. Idesawa %T A System to Generate a Solid Figure from Three View %J BJSME %V 16 %P 216-225 %N 92 %D FEB 1973 %K CADCAM %W 05J %A M. A. Wesley %A G. Markowsky %T Fleshing OUt Projections %J IBM J. Research and Development %V 25 %N 6 %D NOV 1981 As mentioned in AILIST, there are two main methods of modeling objects in CAD/CAM: boundary representations and constructive solid geometry systems. CSG based systems provide some mechanism for converting to boundary representation as this is needed for such functions as display. This can be done in worst case O(N ** 3) time for the two-D case where N is the number of two dimensional objects and O(N ** 4) for three-D. However, the average case is linear! For an extremely clear discussion of these issues, see Tilove's thesis which is TM-38 from the PADL group. Going back from boundary representation to CSG is fairly straightforward. Looking at the problems of conversion from a canonical form perspective or cases where the object is represented parametrically is discussed in my papers. The argument that CSG systems cannot be put on micros is bogus. First of all Cubicomp has been selling a commercial CSG based system for micros for years. Second of all the original research versions of CSG done by the PADL group was done on an 11/40 containing 28K 16 bit words which is much more limited than an IBM-PC.