Cycle shading for the assessment and visualization of shape in one and two codimensions

In this paper we propose cycle shading and hatched cycle shading as new local shading techniques for shape assessment and visualization. Natural surface highlights are extended to not only appear in isolated parts of a surface, but to reappear throughout the surface in a regular and easy-to-control pattern. Thereby even small surface variations become visible, wherever they are located on the surface. We further extend (hatched) cycle shading to curves in 3D, i.e., to shapes of higher codimension. We demonstrate how (hatched) cycle shading improves 3D vector field visualization by showing higher-order discontinuities of streamlines, pathlines, or streaklines. Our visualization approach is generic, simple, efficient, and can readily be used where Phong illumination is applicable because information on curvature or mesh connectivity is not required. The effectiveness of cycle shading for the assessment of surface quality is demonstrated by a user study. Finally, this paper addresses issues of anti-aliasing, parameter control, applications, and efficient GPU implementations. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: 3D Graphics and Realism