ABSTRACT
Most CAD users are familiar with the increasingly sophisticated rendering software which allows the modelling of the effects of light on object surfaces. CAD rendering software allows users to position light sources of various types (e.g. point source, spotlights, ambient sources), and to define the colours, textures, shininess, and other properties of individual surfaces. Once all these factors have been defined, a range of rendering algorithms (computable calculation procedures) such as Gouraud shading, Phong shading, ray tracing and radiosity can be applied to the CAD model. Most rendering systems allow the user to select the method of rendering they wish to use, bearing in mind that the more sophisticated the rendering algorithm, the more computationally intensive are the calculations needed to render the scene. Gouraud shading has the effect of smoothing out the faceted appearance of CAD modelled curved surfaces. Phong shading is better than Gouraud for handling specular reflections (i.e. the reflections from highly polished surfaces). The ray tracing method generates individual rays of light from the CAD model to the viewpoint and can be used to highlight shadows as well as reflections. It is also capable of rendering transparent and translucent objects. The most advanced form of rendering is radiosity, in which each CAD object surface is defined in terms of how much light energy it emits, and how much it reflects.
