ABSTRACT
The design and modelling of three-dimensional objects clearly has many parts. Much effort has been spent discussing representational methods for curves and tensor product surfaces as well as their various attributes which might affect user interaction. An extremely important assumption has been implicit throughout. Design of three-dimensional objects sometimes requires the object to satisfy constraints of a hard kind, such as aerodynamic or hydrodynamic analyses, thermo or stress analyses, or variational constraints. Sometimes there are only aesthetic constraints; they are the most difficult since they are the least analytic. However, all design spirals have a human designer involved. Further, the designer's needs to have a visualization capability must be satisfied. This visualization capability may be needed to see if the computer-generated model really looks the way his internal vision said it should, that is for the geometrical shape, or it may be necessary for the visualization of nongeometric information such as the results of stress analyses, or it may be necessary to see the interaction of the various parts of the model. For all of these reasons visualization methods that allow all levels from the coarse rough look to a high management presentation quality are necessary.
