| OCR Text |
Show Table 2.4. Terms for emergent radiosity solution. Bi Emergent Radiosity- net radiosity leaving surface i Ei Emission Radiosity- luminance of surface i ri Reflectivity - fraction reflected by surface i 12 Fa; Form Factor - fraction of energy leaving surface j to reach surface i which the s~rface emits, Ei. This combination of light leaving the surface is the emergent radiosity Bi· This emergent flux radiates to all the surfaces that are visible from this surface (unoccluded), according to a set of form factors Fii · So we have (as an approximation) n Bi = Ei + ri L B;Fi;, i=l (2.9) where n is the number of surface elements in the environment. To solve for the vector of radiosity values B, the matrix formulation is (2.10) where (2.11) and 6ii is the Kronecker delta. There is an intuitive way to conceptualize the value of a form factor Fii· Consider the two surfaces patches, S, and S;; Fa; is the fraction of the diffuse light emerging from Si to strikeS,. H a tiny hemisphere is constructed on Sj, S, can be projected onto the hemisphere. Going one step further, the projection onto the hemisphere is projected downward - perpendicular to the circular area under the hemisphere. The ratio of this area projected onto the circle to the area of the entire circle is the value F'ai (Figure 2.3). This description of a form factor is called the Nusselt analog. |
