ABSTRACT
The introduction of CAD work at increasingly earlier stages of the design process means that CAD models have to be generated for analysis prior to production models. Analytical models are abstractions of design models, in that they contain the information needed to carry out the analyses. For example, in energy analysis, the composition of materials in the building fabric is of more importance than the precise geometrical shape of the building itself, which can be approximated by closed polyhedral forms. In a design theoretic analysis such as circulation, on the other hand, wall thicknesses become irrelevant, and the topological relationships between spaces take precedence. In the sight-line analysis of the Harbourside project, all elements other than seating and reflecting surfaces are unnecessary. Users of CAD systems need to be able to distinguish between CAD models which are abstractions to be used for analytical purposes, and those which are used for further design development. In mainstream CAD, these distinctions are made by copying files, by referencing files from other files, and by layering. The use of named files and layers can become unwieldy in the case of complex models, and introduce an undesirable level of prescriptiveness if the naming process has been carried out by someone else. What is needed is the ability to represent CAD objects at multiple levels, each corresponding to a different analytical or design aspect. Again, object-orientation offers a way of achieving this, since each of the different views of an object form part of the object’s own representation.
