The catalogue of events defined for solids of revolution has also been used to form aspects of more general curved objects; determining the viewpoints for these visual events is correspondingly harder. Ponce, Petitjean and Kriegman [References: no 4] have presented an algorithm for computing the aspect graph of solids bounded by parametric or implicit smooth algebraic surfaces in orthographic projections.

• Trace the visual event curves
• Eliminate occluded events (opaque objects)
• Construct regions on the view sphere delineated by the remaining events
• Construct corresponding aspects

The size of the aspect graph is 0 (d¹²) where d is the degree of the surface. Therefore, the algorithm can in practice compute the aspect graph only for low degree algebraic surfaces. Some examples are shown in Figure 10, below.

Figure 10: The aspects of piecewise smooth objects

[ Solids of revolution | Summary: the applicability of aspect graphs ]

Comments to: Sarah Price at ICBL.