Example 1: Secondary rays bias

 

Example 1: Secondary rays bias

This example shows the effect of the Secondary rays bias parameter. The scene below has a box object with a height of 0.0, which makes the two sides of the box to occupy exactly the same region in space. Due to this, V-Ray cannot resolve unambiguously intersections of rays with these surfaces. The first image shows what happens when you try to render the scene with the default settings. You can see the splotches in the GI solution, caused by the fact that rays randomly intersect one or the other surface:

 

In the second image below, the Secondary rays bias is set to 0.001, which offsets the start of each ray a little bit along its direction. In effect, this makes V-Ray skip the problemmatic surface overlaps and render the scene correctly:

 

Note that the Secondary rays bias affects only things like GI, reflections etc. In order to render the scene properly, the material assigned to the box has its 2-sided option checked. This is so that the object looks in the same way regardless of whether the camera rays hit the top or the bottom of the box. If the material did not have this option checked, it would appear "noisy" even though the Secondary rays bias is greater than 0.0: