L-reps: 2次元ディスプレイ上で3次元ピンポイントを可能にする2次元指向幾何変換モデル<SUP>*</SUP>

Abstract

In interactive geometric modeling, it is a key operation for a user to specify precisely an arbitrary point of interest in a computer-generated 3D finite work space. We point out that traditional ways of projection transformation have several difficulties in performing the above operation, which is called 3D pinpoint in this paper. In order to alleviate the 3D pinpoint difficulties, we propose L-reps (Lines representations) as a new geometric transformation model for standard 2D displays. L-reps is a 2D drafting-oriented geometric model, and a generalization of conventional lines: a 2D engineering drawing which has been commonly used for the design of ship hulls or automobile bodies. We provide here the data definition and manipulations of L-reps. Also, we present a methodology for utilizing L-reps in a solid modeling environment. Two-way conversion algorithms between B-reps and L-reps are developed as principal components of the hybrid modeling scheme, where precise and aesthetic design tasks can be performed simultaneously. A pilot geometric modeling system is implemented on the basis of the hybrid scheme. The feasibility of our approach is demonstrated with a camera design example on the system.