Patent US 6,233,351

A computerized method of drawing provides sketching-type drawing capabilities in a computer-aided design (CAD) environment. Geometrical drawing parts or elements, sketched through a hand-controlled indicator and lacking in the precision criteria or standards associated with formal drawings, are recognized and interpreted as points, straight lines, open arcs, circles and ellipses. Delete and "areafill" symbols, similarly, are recognized and interpreted. The method also provides the capability to distinguish and interpret relatively complex, multiple-part or element strokes. This is done by determining break locations for the elements along the stroke, and by recognizing these elements before re-constituting a stroke meeting precision criteria. A variety of geometrical constraints which are important in a CAD environment, including coincidence, parallelism, tangency and relimitation, are also recognized and imposed. The recognizing of geometrical elements includes the use of pattern recognition and the use of a neural net. The determination of breaks incorporates the calculation of functions representative of changes in angle, of curvature, and of changes in slope, and the classification of information elements representative of locations, based on such calculations.