Displacement and Trace Bias settings

Getting the displacement to show up correctly using GPSurface with Slim network, you will need to set trace displacement to ON. However, this is not done via adding Renderman Attributes to the shape nodes. Instead, it is set via the Material Ensemble node in Slim. Under Attributes -> Ray Tracing, set Trace Displacements to ON.

One other thing to note here is the Trace Bias (Just under Trace Displacements). It is set at 0.0000 by default, meaning it will use the global value (default at 0.001) found under Render Settings -> Features -> Ray Tracing -> Trace Bias: 0.001. This value may not be what you want as you can see from the renders below. There are few ways you can change the value. The simplest way is to set the global value but this will cause all the geometry to use the same value. I prefer to set it via the Material Ensemble node, so it only applies to any geometry under attached to this material.

Another way is to simply add "Trace Bias" Renderman attributes directly to the geometry shape node. You could also make changes to the Shadow Bias attribute under the Light node but that would be like changing the global Trace Bias value which I am not too sure if that is a good idea.