Basic components of the DIJA project

Abstract

Our goal is to define and implement a web-based CAD System. Distributing a CAD system over the World Wide Web implies that this system has not any knowledge about its user (his computer and CAD skills, his trade, etc.). Thus, this system has to be adapted to each possible user: from neophyte to CAD system expert. Actual CAD systems have complex computer-human interfaces, which are an obstacle to the modeling task for a non-expert end-user. As our aim is to provide a novice end-user with an easy-to-use CAD system, we are interested in providing a more intuitive interface than a classical one. CAD systems propose interfaces based on constructive modeling methods. Creating geometry using these modeling methods, based for example on Constructive Solid Geometry, parametric models or features based modeling, is a very difficult task for somebody who has never used a CAD system. We present in this paper our approach (called synthetic method by opposition to constructive methods) which overcomes this main difficulty by reversing the modeling process. The general idea of our modeling method is that the user chooses an initial crude shape according to the correct object topology. This choice can be done by choosing an existing object or by giving either a functional description or a rough sketch. The chosen shape will be the basis of the modeling task. The user can deform this initial shape by using specific and intuitive dedicated tools, based on surface deformation and on free-form deformation techniques (FFD). This paper deals with the synthetic method concept, its implementation in a dedicated CAD system called DIJA and the improved boundary representation, which is used as geometric model and contains both the visualization model and the dialog model.