The surface roughness feature is an alternative way of generating scatter-like effects on a surface node. Unlike the surface scatter feature, which works by generating a set of rays according to a BSDF, the surface roughness feature works by introducing an element of randomness into the ray intersection/interaction process during the raytrace. A distinguishing aspect of the surface roughness model is that it is not over-ridden by total internal reflection, as is the case with the surface scatter models (i.e. a ray incident on a surface in a TIR condition will not generate scattered rays in transmission). In situations where TIR may be a factor a the surface of interest, the surface roughness model should be used in place of the surface scatter model.
Surface roughness models are applied on a surface by surface basis from the Modifiers tab of the surface's Edit/View dialog.
The surface roughness interaction with a surface is treated as a specular process, not a scatter process. This has important implications when using raytrace path data to diagnose paths through the system which may have involved surface roughness interactions.
The Surface Roughness folder can be found on the left hand side of the FRED document view in the object tree. Mouse clicking the + or - symbol next to the folder on the object tree will expand or collapse the node.
Right mouse clicking on the Surface Roughness folder on the object tree allows selection of the following options:
Summary Report Prints to the output window the name, type, node number and description for all surface roughness models which currently exist on the tree.
Detailed Report Prints to the output window the name, type, active state, overall roughness probability and distribution data for each surface roughness model which currently exists on the tree.
Create New Surface Roughness Node Opens the Create New Surface Roughness dialog and adds a new surface roughness node to the object tree.
Surface Roughness - Sampled Random Surface Normal
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