The ability of a CAD system to perceive a three-dimensional
model depicted in a single freehand sketch presents the
practical possibility of bringing numerous established
analysis tools into the early stages of design to institute
conceptual analysis. In this article we hypothesize that
the key to enabling systems to reason and communicate about
conceptual design is the language of sketching. We explore
this approach, outline the basic algorithms required, and
provide several examples of an implemented system.