Issues on Displaying 3D Data for Scientific Visualization Thomas Theußl theussl@cg.tuwien.ac.at Institute of Computer Graphics Vienna University of Technology Vienna, Austria

Enhancing the perception of layered surfaces

Many applications benefit from displaying multiple surfaces. When these surfaces are depicted opaquely, major parts of the model are occluded. This makes it important to render layered surfaces in such a way, that outer structures can be seen and seen through the same time. Using transparency to show what lies behind or within surfaces can be a useful device. Unfortunately, the shape of transparent surfaces becomes more difficult to perceive accurately, for ordinary depth cues of shading and occlusion are minimally present on them. Adding partly transparent, partly opaque textures to these surfaces achieves perceptual benefits. Several approaches are described below.

• Opacity-modulating Triangular Textures
• Feature Lines
• Curvature-directed Strokes
• Principal Direction-driven 3D LIC textures
• Stream Arrows