Inputting constructive solid geometry representations directly from 2D orthographic engineering drawings

Abstract

A new approach is introduced in this paper to inputting geometric representations of 3D objects via 2D orthographic views. The primitive volumes, out of which the object is built up, such as cuboids, pyramids and spheres, have to be identified and input from an engineering drawing by the user. Their dimensions and transformation parameters are derived by the program from five points input via a digitizer from two to three views of the object. The program then constructs a constructive solid geometry (CSG) representation of the object. The steps of the method follow closely an engineer's train of thought when designing a product or understanding an engineering object by interpreting its orthographic drawings. Not only can this program handle a normal three-view drawing with top, front and side views given in orthographic projections, but it also allows the use of actual engineering drawings given in the following combinations: only two given views; views with cross-sections; views with incomplete projections; or views that follow conventional engineering graphics practice. This program can recognize drawings projected with both the ‘first angle’ and the ‘third angle’ projections which are used in different countries in the world, and it can handle both planar polyhedral volumes (cuboids and tetra pyramids) and volumes with simple curved surfaces (cylinders, cones and spheres). In the present state of development of the program, the axes of those volumes can be perpendicular to one of the projection planes, or oblique to two of them.