There are three principal ways to obtain a BRDF. We can
- Derive an analytic formula using physical principles
- Use simulation given an assumed or measured model of the surface microgeometry
- Measure the BRDF based on empirical observation
A number of analytic formulae have been proposed for BRDFs. Many Formulae have been derived from physical principles. A number of models such as the Torrance-Sparrow model have been derived from the distribution of microfacet orientations. One may postulate a certain microgeometry for the surface, and simulate the resulting BRDF by using a software raytracer.
Once the scattering of light on a surface is understood how is a reflectance function derived? Can anyone recommend any resources on this topic?