Doi: 10.1145/2398356.2398378

technical Perspective
Visualization, understanding,
and Design

By Doug DeCarlo and Matthew Stone

 

PhotoGRAPhs CAPtuRe the moment; paintings convey perception, impression, and feeling; illustrations tell stories. Computer graphics aims to enrich all these artistic practices through technology. The following paper is a watershed in depiction, creating imagery that gets ideas across. Mitra et al. describe an interactive system that analyzes the operation of mechanical devices and explains them visually to users. Their compelling results showcase an innovative synthesis of newly mature techniques for robust analysis of 3D geometry and for domain-specif-ic information design.

Like many watershed papers in computer graphics, this paper takes its cues from the work of a master artist—in this case, RISD Professor and MacArthur Fellow David Macaulay. While Macaulay may be best known for the engaging and richly informative visual storytelling of his architectural history books Cathedral and Castle, the authors here base their system on his book The Way Things Work. It is a fascinating compendium of explorations of everyday artifacts, like the lock on your front door, illustrated through lucid visual explanations that communicate a deep understanding. Such pictures are the authors’ inspiration.

They get their understanding of
the world through geometry. They do
not simulate physics directly. They
use symmetries to infer how compo-
nents might move; they use correspon-
dences to recognize components that
can drive one another. The geomet-
ric computations allow approximate
matches, by exploiting the robust sta-
tistical principle that reliable symme-
tries and correspondences leave lots
of evidence. So a first step searches for
candidate matches, and a second step
tabulates the results to find consistent
patterns. Such techniques have a long
history, but recent bridges to comput-
er graphics have had an enormous in-
fluence on the practical analysis of 3D
shape, as you see here.

the following
paper is a watershed
in depiction,
creating imagery
that gets
ideas across.

analysis of exemplary hand-made work, from artists’ reflection on their practice, from psychological theories of how people understand these visualizations, and from the researchers’ own experimentation with the possibilities of technology.

Realizing these design principles involves a judicious choice of visual techniques. Non-photorealism in computer graphics offers diverse ways to stylize appearances and guide the viewer’s attention. Examples include modulations of detail and weight in rendering objects, the use of cutting and transparency to depict objects in multiple layers, and even selective choices about which elements to render at all. The use here of simple line drawings, with arrows for annotation, and a constrained set of highlighted parts and exploded views, is a choice that reliably leads to clear and uncluttered imagery. To create accessible imagery with more richly varying rendering techniques, or with visualizations of additional information (forces, for example), it might be necessary to develop much more nuanced design principles. The pictures here, however, are clearly a success.

It is never easy to endow computers with a deep and interesting understanding that they can share with their users. But that does not mean we should regard inference as hopeless or design as magic. As this work shows, general tools and methodologies are making it easier and easier for systems to communicate the understanding they have through clear and compelling visualizations. The results here thus take on particular significance as a benchmark in visual explanation, and a model for future systems.

 

Doug DeCarlo ( [e-mail]) and Matthew Stone ( [e-mail]) are associate professors in the department of Computer science and Center for Cognitive science at Rutgers university, Piscataway nj. deCarlo is currently on leave at Google, Inc.

© 2013 aCM 0001-0782/13/01