Geometric primitives (cone, cube, cylinder, diamond, pyramid, sphere, tetrahedron, torus) modified from here: http://web.mit.edu/djwendel/www/weblogo/shapes/basic-shapes/
Each primitive has min z = 0 and max z = 1.
procedural_generation.py allows one to make multilink urdfs from these primitives, dumping files in a style similar to the partnet-mobility urdfs.