Design is a subjective and iterative process. To date, computers have served designers primarily in accelerating engineering and presentation tasks. Software programs for precise two-dimensional drafting and three-dimensional modeling produce construction documents, photo-realistic images and interactive visualizations of a finalized design solution. Unfortunately, few applications exist that truly support the more creative endeavor of early conceptual design.

We introduce a new paradigm for computer-based conceptual design. We have developed a
system that allows a designer to freely draw on the surface of a large design table that is both a pen-based digitizer and computer display. These freehand strokes, drawn directly onto the
computer display, are projected into the application's virtual space to become the primary
elements of a sketch-model - a three-dimensional drawing.

By using the tabletop projection surface, combined with the photorealistic rendering software
developed at the Program of Computer Graphics, we have provided a means for the architect to sketch directly into a realistically simulated three-dimensional virtual environment. This capability spans the preliminary and final design stages, providing immediate visual feedback for design modifications and decisions.

Our system thus simultaneously provides the means for loose and ambiguous freehand drawing
and precise and robustly define representations.

Lastly, our system provides a framework in which several designers can converse verbally as well as graphically while working in a shared virtual model space from geographically remote locations.