Freehand sketch system for 3D geometric modelling

The 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 in the design procedure. The designer can keep the 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. The interactive methods are suitable for realistically constructing any geometric shapes that a designer imagines. Created data are transferred to an advanced 3D-CAD system. The system is applied as a front-end processor of design practice in fields such as office equipment.