Mitchel Clayton


RenderMan Secondary Geometry

This project displays the usage of Pixar's custom MEL procedures to create additional geometry at render time. It also creates a custom UI within maya to enable artists to easily use. All of the vegetation in the following scene was created using these scripts. If you hover over the images below you can see the scene without the Secondary Geometry.

RIB Archives

UI Breakdown

Below is a breakdown of the various elements of the UI and how it works with secondary geometry.

Default values plus random archive.

Align objects to normals

Min Scale = .3

Max Scale = .8

Jitter = .3

Offset = .5

Remove Geometry Percentage = 50%

Cull based on Y Normal

Cull angle = 0

Cull angle = -0.2

Cull angle = 0.8

Density map turned on

Density = 100;

Uses map below








Problems &  Solution

I wanted to have more control over the positioning of the secondary geometry but was not able to find an easy way to create density maps on poly surfaces. A solution to this was to check the Y axis of the normal at each vertice. With this I was able to control whether I wanted objects to populate on vertices based on there Y normal. I created a slider that could decided the angle at which it would cull the objects. the base setting was 0. so anything lower then an Y normal of 0 would not be placed at render time.


Working with RiMEL is a lot of fun and a very powerful tool. If I had more time I would also have like to add the ability to use texture maps on poly surfaces to create density maps and then have more control over the placement of the geometry. This would allow a lot more fine tunning of the positioning of the the secondary geometry.


Additionally I would like to add the option to be able to select the folder that is used for the random archive as well as adding additional archive options to allow for more variety in the objects that are placed on the mesh.