The use of drawing in design processes is well-documented [Do
2002; Bae et al. 2003; Bae and Kijima 2003; Buxton 2007]. In
the early ideation stages of design, sketching is largely an artifact
of visual thinking. Often a designer will generate tens of freehand
sketches per hour, most of which are discarded. Once a conceptual
design has been selected, final production drawings are carefully
constructed for presentation to clients or management, and
then passed on to trained modelers who translate the drawings into
3D models using tools such as Alias Studio [Autodesk Inc. 2009].
Design drawing guidebooks [Ching 1997; Robertson 2003] describe
in detail how drawing systems facilitate the translation of
concept sketches into final drawings. Drawing systems such as
two-point perspective, isometric, and elevation oblique, are sets of
heuristic rules which allow viewers to accurately interpret straight
lines in the drawing. Curves fall outside the rules of drawing systems,
but the ambiguity of a curve can be reduced by indicating
intersection or tangency constraints with lines that are well-defined.
Analytic drawing is a mechanical process for depicting a 3D
form [Ching 1997]. Using a drawing system, the designer first constructs
a scaffold of regulating lines which express 3D relationships
in the drawing (Figure 2). These guidelines act as contextual constraints
for drawing curves, allowing them to be sketched with enhanced
accuracy. [Schmidt et al. 2007] discussed visual scaffolding
in more general artistic contexts, of which analytic drawing scaffolds
can be considered a subset. Figure 2 shows some examples
of analytic drawings with the scaffold still intact. We rarely see
these drawings because it is common practice to finish production
drawings by tracing the feature curves onto another piece of paper.