Why does the Fresnel term use the incoming direction and the half vector instead of the normal?

Shruteek

This model requires a pre-existing understanding of the roughness, normal distribution, and general surface properties of the material being modeled. Given the underlying complexity, I imagine that characterizing materials to get these terms is difficult, since it's all dependent on how the object is realistically created/machined/processed/obtained. If we have a modeling program, then, and we want to make a new object of some material, like wood, how would we get these terms for that object's surface without actually having made it in real life? Do we have to define default values or formulas for these terms for each material? Would that even be accurate across different macroscopic geometries?

geos98

@yzliu567 my understanding is this term describes reflection, and the half vector is the vector that light is reflected on.

Why does the Fresnel term use the incoming direction and the half vector instead of the normal?

This model requires a pre-existing understanding of the roughness, normal distribution, and general surface properties of the material being modeled. Given the underlying complexity, I imagine that characterizing materials to get these terms is difficult, since it's all dependent on how the object is realistically created/machined/processed/obtained. If we have a modeling program, then, and we want to make a new object of some material, like wood, how would we get these terms for that object's surface without actually having made it in real life? Do we have to define default values or formulas for these terms for each material? Would that even be accurate across different macroscopic geometries?

@yzliu567 my understanding is this term describes reflection, and the half vector is the vector that light is reflected on.