Given a set of bottom-level acceleration structures, the applicationthen defines a set of instances (by pointing toD3D12_RAYTRACING_INSTANCE_DESCstructures living in GPU memory). Each instance points to a bottom-levelacceleration structure and includes some other information forspecializing the instance. A couple of examples of the specializinginformation included in an instance definition are: a matrix transform(to place the instance in the world), and a user defined InstanceID(identifying the unique instance to shaders).