This thesis addresses real-time non-photorealistic rendering techniques and their applications in interactive visualization. Real-time rendering has emerged as an important discipline within computer graphics developing a broad variety of rendering and optimization techniques along with dramatic advances in computer graphics hardware. While many applications of real-time rendering techniques concentrate on achieving photorealistic imagery, non-photorealistic computer graphics is investigating concepts and techniques that deliberately abstract from reality using expressive, stylized, or illustrative rendering; major goals include visual clarity, attractiveness, comprehensibility, and perceptibility in depictions. Non-photorealistic rendering techniques often rely on the concepts and principles found in traditional illustrations, graphics design, and art.

The contributions of this thesis include three general-purpose real-time non-photorealistic rendering techniques:

• The edge-enhancement rendering technique accentuates visually important edges of 3D models facilitating the effective communication of their shape. The technique takes an image-space approach for edge detection and encodes the resulting edge intensities as texture, called edge map, to enhance 3D models on a per-object basis.
• The blueprint rendering technique extends the edge-enhancement technique to the 3D models´ occluded parts to accentuate their visible as well as their occluded visually important edges. Vivid and expressive depictions of complex aggregate objects become possible that facilitate the visual perception of spatial relationships and let viewers obtain insights into the models.
• The sketchy drawing rendering technique stylizes visually important edges of 3D models. Depicting 3D models in a sketchy manner allows us to express vagueness and is vitally important for communicating ideas and for presenting a preliminary, incomplete state.

Two applications based on these real-time non-photorealistic rendering techniques in the fields of visualization demonstrate their ability to build compelling, interactive visual interfaces:

• Illustrative 3D city models apply non-photorealism to represent virtual spatial 3D environments together with associated thematic information. The abstracted, stylized depiction emphasizes components of 3D city models and thereby eases recognition, facilitates navigation, exploration, and analysis of spatial information.
• Illustrative CSG models apply non-photorealism to image-based CSG rendering. They enable us to visualize the design and assembly of complex CSG models in a comprehensible fashion. It also simplifies the interactive construction of CSG models.

Finally, the thesis investigates an automated approach to depict dynamics as a complementary, important dimension in information contents by means of non-photorealistic rendering:

• The smart depiction system automatically generates compelling images of a 3D scene´s related dynamics following the traditional design principles found in comic books and storyboards. The system symbolizes past, ongoing, and future activities and events taking place in and related to 3D scenes.

The non-photorealistic rendering techniques and exemplary applications presented in this thesis demonstrate that non-photorealistic rendering serves as a fundamental technology for expressive and effective visual communication and facilitates the implementation of user interfaces based on illustrating 3D scenes and their related dynamics in an informative and comprehensible way.

downloadable thesis (pdf format)