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A system for the automatic generation of line illustrations of three dimensional sculpted objects is described. In particular, a enriched vocabulary of lines are defined which provide a means to impart meaning to visual representations of complex objects. Particular attention is paid to how the end conditions of individual segments effect how they are drawn. A graphical interface is described for creating illustration rules which translate the geometric description into the final drawing. Some algorithmic details are provided for implementation and preliminary results are presented.

This paper developes a system for automatically generating 2D illustrations from 3D geometric models. The 3D geometric model, as displayed by the Alpha_1 modeling system, uses hidden line and surface removal, as well as shading to create either wireframe, or realistically shaded depictions of the model. However, the intellegent use of lines is needed to more clearly convey the shape of the model, especially when output to 2D. Technical illustrators use line characteristics to convey information about a scene. Such attributes include line width, end conditions, as well as using dotted and dashed lines. Adding these attributes to lines in an illustration expresses spatial information, however these attributes must be assigned to lines depending on the viewpoint of the scene, rather than a global assignment. Thus, the Alpha_1 system is used to identify hidden lines and surfaces, and this information is used to intialize a user interface in which the user can specify importance of lines, driving the automatic creation of the 2D illustration. From the hidden line and importance information, the system infers the thickness of the line (which can vary based on depth), end point conditions (thickening and tapering), and attributes of dashed and dotted lines. These attributes then allow for a more meaningful 2D illustration to be created.

2D line illustrations, line attributes

@InProceedings{	dooley:1990:AIGM,
author =	"Debra Dooley and Michael F. Cohen",
title =	"Automatic Illustration of 3D Geometric Models: Lines",
booktitle =	"Proceedings of the Symposium on Interactive 3D Graphics",
pages =	"77--82",
year =	"1990",
}

1. Elber, Gershon and Elaine Cohen, Hidden Curve Removal for Free form Surfaces, Technical Report, Dept. of Computer Science, University of Utah, 1989
   
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3. Thomas, T.A., Technical Illustration, 2nd Ed., McGraw Hill, Inc., 1968.