Freehand Sketch System for 3D Geometric Modeling

This paper introduces a new method to deal with sketches for inputting geometric models at a workstation. The sketches are drawn on a CRT screen through a stylus pencil and a tablet by a designer at an early stage of design procedures. He can keep their drawing stylus at a workstation as the same manner as using a pen on paper. The system `Sketch Interpreter' can correct geometric models in a computer even though input sketches are geometrically distorted. This system can create 3D geometric models in a computer even though input data of 2D sketches are drawn by freehand. The system is constructed in terms of three characteristic procedures on a workstation with a pointing device ; (1) to recognize hand sketches on the screen. Freehand lines are drawn by pen operations from which a computer can construct a 3D geometric model. The first operation computes mathematical parameters for the projective transformation; (2) to construct additional geometric models by inputting more sketches drawn perspectively; and (3) to redraw modified geometric models replacing the sketch lines. Our interactive methods suit to realistically construct any geometric shapes a designer imagines. Data created are transferred to an advanced 3D-CAD system. Our system is applied as a front-end-processor of design practice such as for office equipments.