  Heterogeneous object design is an active research area in recent years. The
conventional CAD modeling approaches only provide geometry and topology of the
object, but do not contain any information with regard to the materials of the
object and so can not be used for the fabrication of heterogeneous objects (HO)
through rapid prototyping. Current research focuses on computer-aided design
issues in heterogeneous object design. A new CAD modeling approach is proposed
to integrate the material information into geometric regions thus model the
material distributions in the heterogeneous object. The gradient references are
used to represent the complex geometry heterogeneous objects which have
simultaneous geometry intricacies and accurate material distributions. The
gradient references helps in flexible manipulability and control to
heterogeneous objects, which guarantees the local control over gradient regions
of developed heterogeneous objects. A systematic approach on data flow,
processing, computer visualization, and slicing of heterogeneous objects for
rapid prototyping is also presented.
