Non-Photorealistic Rendering Research

Real-time Principal Direction Line Drawings of Arbitrary 3D Surfaces Ahna Girshick Victoria Interrante Computer Graphics Visual Proceedings (ACM SIGGRAPH 99 technical sketch), p.271. Download PDF (1MB) Abstract In the field of computer-generated line drawings, line direction is among the most critical factors for conveying surface shape. Principal direction line drawings generated from volume data inspired us to target the widely-used polygonal surface representations. We use the principal directions of curvature to guide the lines over an arbitrarily curved 3D surface. The resulting line drawings are viewpoint independent and can be rendered in real-time.

Line Direction Matters: An Argument for the Use of Principal Directions in 3D Line Drawings Ahna Girshick Victoria Interrante Steve Haker Todd Lemoine First International Symposium on Non Photorealistic Animation and Rendering (NPAR 2000), Annecy, France, June 5-7 2000, p.43-52. Download PDF (6.2MB) Download "gzipped" (for unix) PDF (1MB) Download "winzipped" (for windows) PDF (1MB) AVI Animation (5.8MB) The animation demonstrates how geometrically invariant lines stick the surface (no jitter) and how principal directions convey curvature. Abstract While many factors contribute to shape perception, psychological research indicates that the direction of lines on the surface may have an important influence. This is especially the case when other techniques (shading, silhouetting) do not present sufficient shape information. The psychology literature suggests that lines in the principal directions of curvature may communicate surface shape better than lines in other directions. Moreover, principal directions have the quality of geometric invariance so line directions are based on the surface geometry and are viewpoint and light source independent, and the lines do not move above over the surface during animation unless desired. In this work we describe principal direction line drawings which show the flow of curvature over the surface. The technique is presented for arbitrary surfaces represented by either 3D volume data or a polygonal surface mesh. The latter format is common in the field of computer graphics yet thus far has not been widely used for principal direction estimation. The methods offered in this paper can be used alone or in conjunction with other NPR techniques to improve artistic 3D renderings of arbitrary surfaces.