Doctor of Philosophy

dissertationIn this dissertation a group of interactive volumetric rendering algorithms are presented that aim to increase the effectiveness of visualizations of scientific data sets arising in many varied fields such as radiology, chemistry or simulations of physical phenomena. Interactivity is an important aspect of a visualization system since it permits rapid exploration and visual analysis of the relevant data sets and as such avoiding costly pre-computations is of key importance. The volume shading methods presented in this dissertation were designed to account for this and to enable interactive visualizations of volumetric and geometric data sets by exploiting the parallel computing powers available on modern graphics processing units. The presented volumetric directional occlusion shading method allows computation of a subset of the global ambient occlusion solution by restricting the occlusion computation to a viewer oriented cone. This enables an efficient implementation in a slice-based direct volume rendering system, while at the same time providing plausible depth cues similar to those of a full ambient occlusion computation. The presented rendering of combined occlusion effects from both volumetric and geometric structures extends the benefits of enhanced depth perception to data sets combining geometry and volumes. Those originate in many varied fields of scientific visualization, where tube shaped structures are situated within an associated scalar volume. Common examples are DTI fiber tractography or streamline tracing. The method for computing depth of field effects presented in this dissertation supports an alternative way of providing supplementary depth cues within the context; of direct volume rendering. They are especially useful for data sets, such as those arising from combustion simulation, where the presented occlusion shading method is less effective due to lack of sufficiently opaque, surface-like structures. This dissertation also discusses a GPU implementation of a recently presented analytical scattering model which enables the computation of single scattering effects in homogeneous participating media with anisotropic phase functions and light distributions. The interactive computation of those scattering effects are used in interactive entertainment applications to compute volumetric lighting, but also in programs that simulate visibility of traffic signs under adversary visibility conditions, such as smoke, fog or heavy rain