Scatterers - Extended Harvey Shack

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Extended Harvey-Shack

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Description

The Extended Harvey-Shack scatter model, developed by Alan W. Greynolds, is a variation of the standard Harvey-Shack scatter model that adds a dependence on the angle of incidence by using the functional form:

In the equation above,

q = scatter angle with respect to the surface normal coordinate system

q₀ = specular angle with respect to the surface normal coordinate system

b = sin(q)

b₀ = sin(q₀)

The two |b - b₀| plots below show the behavior for an Extended Harvey-Shack model with parameters b0=0.1, L=0.01, S=-1.5, P = 2, Q = 1 and a standard Harvey-Shack with parameters b0=0.1, L=0.01, S=-1.5. Note that all of the curves of the standard shift-invariant Harvey-Shack model fall on top of each other while the variation on the specular angle is exhibited in the Extended Harvey-Shack by a separation of the curves. Furthermore, notice that there is a distinct "tail" in the Extended Harvey-Shack model that is not present in the standard Harvey-Shack representation.

Navigation

This feature can be accessed by selecting Extended Harvey-Shack (polished surface scatter) as the Scatter Type in the Create a new scatter model dialog box.

Controls

Control	Inputs / Description	Defaults
Name	Name of the model (required).	Scatter n
Description	Description of the model (optional).
Type	Select Extended Harvey-Shack from the pull down menu.	Lambertian
Parameters
b0	Value of the BRDF at b = b₀ (towards specular). The value of b₀ must be greater than 0 and is typically between 0.001 and 10.0.	0.1
L	Value of the near specular BSDF rollover (knee) point at L = b - b₀. The value of L must be greater than 0 and is typically between 0.001 and 0.2.	0.01
S	Slope of the BSDF at large b - b₀ (away from specular). The value of S must be less than 0 and is typically between -0.5 and -3.0.	-1.5
P	Power of g (see equation above) in the near specular BRDF term.	2
Q	Power of g (see equation above) in the rollover term.	1
Additional data
Apply on Reflection	Apply the scatter model on reflection.	Checked
Apply on Transmission	Apply the scatter model on transmission.	Unchecked
Halt Incident Ray	For any surface with this scatter model assigned to it, no specular rays will leave the surface, regardless of the surface coating and raytrace property settings, if this toggle is checked.	Checked

OK	Accept settings and close dialog box.
Cancel	Discard settings and close dialog box.
Help	Access this Help page.