The capabilities of current solid modelling systems are limited by the available representation schemes, geometric coverage, and types of operations allowed within a modelling system. Most of today's modellers can hardly do anything beyond graphic display and mass property calculation. Modelling systems need to extend their representations, geometry and operations to enable them to meet the requirements of the variety of engineering applications.
This paper addresses the introduction of a class of operations called offsetting into solid modelling environments. A range of potential applications that could benefit from an offsetting utility has been identified, and a formal mathematical framework that rigorously characterizes the offsetting function is developed. solid modelling, offsetting, computational geometry Tied to the development of solid modelling techniques over the last two decades have been great hopes that once correct and valid geometrical representations were developed, many of the problems in mechanical design and manufacture, such as mesh generation for finite element analysis and generation of numerical control (NC) code, that require some form of geometric information could be easily solved in a fully or semi-automated manner. This proposition was based on the fact that solid modelling systems are informationally complete I and are capable, in theory, of answering any well-defined geometric question.
Consequently, research efforts have been concentrated on devising valid and useful geometric representation schemes 2'3. As soon as this had been reasonably achieved, it became apparent that obtaining the appropriate geometric information from the representations, often called interrogating solid models, is a much harder problem. A basic modelling system with only the Boolean operations is of little help when it comes to applications other than graphic display unless other utilities to interrogate the geometry, perform some intermediate evaluations, and simulate physical processes are included in the system.
A typical useful modelling system contains core algorithms that are used by the different application programs to perform low level geometric calculations, e.g. curve/ surface intersection, and application specific algorithms tailored to satisfy the requirements of the particular applications.
Algorithms that could be invoked by the application commands are of two general types: Geometric Modelling Project, Department of Mechanical Engineering, The