ABSTRACT
This chapter describes the body-and-cad rigidity model, defined to capture the majority of systems specified by this type of computer aided design (CAD) software: a body-and-cad framework is composed of rigid bodies with pairwise coincidence, angular or distance constraints between them. It also describes the combinatorial counting property that characterizes generic infinitesimal rigidity of a subset of body-and-cad frameworks. The chapter presents schematic for the pattern of the rigidity matrix highlighting the distinction between angular and blind constraints. The building blocks of a body-and-cad framework are fully dimensioned rigid bodies with no internal degrees of freedom, such as a chair leg in 3D. In CAD software, users often work in a 3D "assembly" environment, which can be modeled as a body-and-cad framework with rigid bodies for the "parts" and geometric constraints for the "mates." A rigid body-and-cad framework is minimally rigid if the removal of any primitive constraint results in a flexible framework.
