shaderball.obj and shaderball.mtl are derived from the StandardShaderBall
asset published by the USD Working Group, which is licensed CC-BY-4.0:
https://github.com/usd-wg/assets/tree/main/full_assets/StandardShaderBall
Credit: Chris Rydalch (geometry and textures), André Mazzone (specification and validation), Thomas Anagnostou (original scene and inspiration).
The original USD asset was imported into Blender 3.4.1 and re-exported as
Wavefront OBJ + MTL for testrender, which triangulates the mesh and drops the
shading networks. The exported .mtl retains the original material names, which
testrender uses to assign OSL shader groups.
Additional geometry in the form of emission planes were added in place of USD area
lights, which cannot be represented in OBJ format and which testrender can not use.
These are the emitterTop0 through emitterTop3 and emitterLeft0 groups. The
modeled geometry is otherwise unchanged.