What are the Specific needs for realism

The graphical representation of solids are better dealt in 3-D graphics for visualization,  which had to take the mathematical model and line representations typically as and bring them up to the realism of the real world, which meant the following :

(a) Most real objects are opaque, and we only see the lines and surfaces at front.  Those portions at the back had, therefore, to be eliminated from the mathematical model before plotting. We will discuss this under "Hidden-Line and Surface Removal", which can also be referred to as Visible Surface Identification.

(b) All real objects appear smaller as they are farther from us, with parallel lines converging away from us. Hence, except for construction and fabrication drawings and scientific graphs, which should avoid spatial distortion, perspective projection as in Figure 3.1(c) should be preferred for all 3-D viewing. We will discuss this under "Perspective Projection".

(c) All real objects exhibit surface characteristics due to two causes, namely the surface textures, and the effect of the light falling on them. Thus, blank areas or flat shades of gray or colour must be enhanced to simulate actual surfaces. We shall discuss this under "Surface Renderings".