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St. Mantler:
"Interactive Vegetation Rendering";
Supervisor, Reviewer: H. Hauser, W. Purgathofer; Institut für Computergraphik und Algorithmen, TU Wien, 2007; oral examination: 2007-03.

Vegetation poses a significant problem to computer graphics because the
geometric complexity of plants does not lend itself very well to traditional
simplification approaches. This thesis presents new algorithms
that address these issues at different scales, for rendering individual plants
as well as entire landscapes.
For individual plants we introduce Displacement Mapped Billboard
Clouds, an extended version of the billboard cloud extreme simplification
approach. Billboard clouds have been successfully used to reduce the
geometric complexity of highly detailed models to a few planes, however
the resulting models are often unsuitable for viewing at closer distances.
The presented extension exploits shaders to improve the visual quality
of the resulting models.
Also, a method is introduced for quickly determining approximate
visible sets for point clouds, which are often used for rendering individual
plants. Approximate visible sets allow a significant reduction in the
number of primitives to be rendered with only very little impact on visual
quality.
For entire landscapes, displacement mapping shaders are explored to
enhance existing terrain models with vegetation. We also address the
issues involved with applying such techniques at a global scale, and
present the integration of our method in the open source World Wind
geospatial viewer.
Furthermore, we propose a way to enable early-Z acceleration methods
on the GPU for shaders where this is not yet possible, and discuss the
handling of level of detail validity and criteria for time-critical rendering
of discrete and continuous levels of detail.