Trace Sets

Introduction

Trace Sets allow fine-grained control of what objects can be seen through reflections and refractions. For example, using Trace Sets, you can set the reflections on a particular object to include only a subset of the objects in the scene without affecting the reflections elsewhere in the scene.

A Trace Set represents a group of objects or a set. For covenience, Trace Sets can be configured to be Inclusive or Exclusive:

An inclusive Trace Set represents the set of objects in the Trace Set.
An exclusive Trace Set represents all objects in the scene except those objects in the Trace Set.

Reflection Trace Set

To better understand and visualize how Trace Sets work, consider the example below. On the left, the scene is rendered without Trace Sets. On the right the same scene is rendered but with an Exclusive Trace Set containing the red box assigned to the "Reflection Trace Set" attribute of the reflective mirror wall.


Beauty render with no Trace Sets.	Beauty render with an Exclusive Trace Set containing the red box assigned to the Reflection Trace Set attribute of the mirror wall. The reflection of the red box is now missing from the wall while the other objects are still reflected.

Refraction Trace Set

In this next example we have asigned an Exclusive Trace Set to the 'Refraction Trace Set' attribute of the glass cube object. The objects in the Exclusive Trace Set (the red box in this example) are not being included in the glass cube's refractions.


Beauty render with no Trace Sets.	Beauty render with an Exclusive Trace Set containing the red box assigned to the Refraction Trace Set attribute of the glass cube. The refraction of the red box is now missing from the glass cube while the other objects are still visible.

Creating Trace Sets

Trace Set Options

When a Trace Set is in exclusive mode, reflection or refraction rays are visable for all objects in the scene except the objects in the Trace Set.

When a Trace Set is in inclusive mode, reflection or refraction rays are visable for only the objects in the Trace Set and all other objects are excluded.

Reflection Exclusive & Inclusive Modes

The red cube is in the Trace Set for the back wall's "Reflection Trace Set." The red cube is now missing in the reflection when using "Exclusive Mode."

The Trace Set is now using "Inclusive Mode" where all other objects in the scene except the red cube are ignored from the reflection even the ground plane.

Refraction Exclusive & Inclusive Modes

The red cube is in the Trace Set for the Glass cube's "Refraction Trace Set." The red cube is now missing in the refraction when using "Exclusive Mode."

The Trace Set example below is now using "Inclusive Mode" where all other objects in the scene except the red cube are ignored from the reflection, even the ground plane and the glass cube itself. This will make it look strange in some situations but is actually the correct response.

In order to make the result more "pleasing" we need to also account for the glass cube and ground plane by including them into the Trace Set along with the red cube. This will result in the blue cube being removed from the refraction while also accounting for the refractions from the ground plane and glass cube itself.


This result looks strange because every object except the red cube is missing from the refractions including the refractive glass cube itself.	By also including the ground plane and the glass cube into the trace set along with the red cube we end up with a more pleasing image which removes all other objects from the glass cubes refraction. In this example the blue cube is now missing from the refraction and looks approriate.

When using Inclusive Mode on the Refraction Trace Set of a refractive object make sure to include the refractive object itself or you will get unappealing results.