Peabody uses the term environment to refer to the entire world of geometric
objects. The environment consists of individual gures, each of which is a
collection of segments. The segments are the basic building blocks of the
environment. Each segment has a geometry. It represents a single physical
object or part, which has shape and mass but no movable components. The
geometry of each segment is represented by a psurf, which is generally a
polyhedron or a polygonal mesh but can be of a more general nature.