A Projective Approach to Computer-Aided Drawing
Author(s): Osama Tolba.
PhD Thesis: Massachusetts Institute of Technology,
2001.
[BibTeX]
Abstract:
I present a novel drawing system for composing and rendering perspective scenes.
The proposed approach uses a projective two-dimensional representation for primitives
rather than a conventional three-dimensional description. This representation
is based on points that lie on the surface of a unit sphere centered at the viewpoint.
It allows drawings to be composed with the same ease as traditional illustrations,
while providing many of the advantages of a three-dimensional model. I describe a
range of user-interface tools and interaction techniques that give the drawing system
its three-dimensional-like capabilities. The system provides vanishing point guides
and perspective grids to aid in drawing freehand strokes and composing perspective
scenes. The system also has tools for intuitive navigation of a virtual camera, as
well as methods for manipulating drawn primitives so that they appear to undergo
three-dimensional translations and rotations. The new representation also supports
automatic shading of primitives using either realistic or non-photorealistic styles. My
system supports drawing and shading of extrusion surfaces with automatic hidden
surface removal and emphasized silhouettes. Casting shadows from an infinite light
source is also possible with minimal user intervention. I describe a method for aligning
a sketch drawn outside the system using its vanishing points, allowing the integration
of computer sketching and freehand sketching on paper in an iterative manner. Photographs
and scanned drawings are applied to drawing primitives using conventional
texture-mapping techniques, thereby enriching drawings and providing another way
of incorporating hand-drawn images. I demonstrate the system with a variety of
drawings.
A Projective Drawing System
Osama Tolba, Julie Dorsey, Leonard McMillan.
2001 ACM Symposium on Interactive 3D Graphics,
2001. [BibTeX]
Sketching with Projective 2D Strokes
Osama Tolba, Julie Dorsey, Leonard McMillan.
UIST '99,
1999. [BibTeX]