| OCR Text |
Show 114 The determination of the reflected intensity is carried out in terms of the directions of certain vetors in the scene. The three most important are N, then vector normal to the surface, L, the ,vector pointing from the surface in the direction of the light source, and E, the vector pointing from the surface to the eyepoint. In all cases, these vectors are assumed to have been normallized (have length equal to 1). In addition, the normal vector N can point in either of two opposite direction depending on the way the surface was defined. For consistency, we will assume that the direction is chosen which yields a positive dot product with the eye direction E. These vector directions are illustrated in figure 40. Figure 40 - Vector Directions Determining Reflectivity A simplification that is often made is to assume that the light source is at infinity. Thus the vector L is the same for each point of the picture. The eye is also commonly modelled as being far away from the object so that |
