- Class Moby::Gears  
- implement a rest position for q?  
- Class Moby::Joint  
- implement a rest position for q?  
- Class Moby::PrismaticJoint  
- implement a rest position for q?  
- Class Moby::RigidBody  
- implement rest matrix  
- Member Moby::UnilateralConstraint::write_vrml  (const std::string &filename, double sphere_radius=0.1, double normal_length=1.0) const 
- add a cone onto the arrows