Trace Set - Arnold for Houdini
It is possible to designate objects to be part of one or many trace sets. T he trace_set shader marks specific rays with an inclusive or exclusive trace set.
With the Arnold Visibility Geometry Properties it is possible to tag objects to be part of one or many trace sets.
Example
Below is a shading network for a floor material which segregates shadow and specular rays into two different trace sets:
The sphere objects are then tagged to be part of the shadows or specular or both trace sets: