CAGD - computer-aided gravestone design

Although the title may seem facetious, the design of objects other than mechanical objects illustrates the same principles that drove the early shape modelling developments. The so-called 'local operations' were originally developed to provide specific local changes to models. These were quicker and less expensive than performing the operations using Boolean operations which performed global checks. Later, the notion of locality disappeared as specialised operations were developed for operations such as reflection (symmetry) and, still later, shelling. Although performing global changes, these operations were implemented as sequences of localised changes. The common factor between the original local operations and the later specialised operations was, and is, that they perform conceptually specific changes. The justification for developing these modelling tools is that they allow the user to perform shaping operations in a more natural manner avoiding the necessity of reformulating the intended change in terms of general tools, such as the Boolean operations. The problem is for the software developers that the number of such local or specific operations is unlimited; it is not possible to create a complete set. The type and functionality of these operations depends on the application, hence they need to be developed separately for different application areas, which in turn implies that the development costs have to be shared between a subgroup of the CAD clients, which means that they may be too expensive to justify in commercial terms. This paper describes some of these special operations that may be useful for designers of stone products, for gravestones or for kitchens, for example. (C) 2005 Elsevier Ltd. All rights reserved.