Stereoscopic, Real-time, and Photorealistic Rendering of Natural Phenomena - A GPU based Particle System for Rain and Sno

Natural phenomena exhibit a variety of forms such as rain, snow, fire, smoke, fog, and clouds. Realistic stereoscopic rendering of such phenomena have implications for scientific visualization, entertainment, and the video game industry. However, among all natural phenomena, creating a convincing stereoscopic view of a computer generated rain or snow, in real-time, is particularly difficult.Moreover, the literature in rendering of precipitation in stereo is non-existent and research in stereo rendering of other natural phenomenon is sparse. A survey of recent work in stereo rendering of natural phenomenon, such as vegetation, fire, and clouds, is done to analyze how stereoscopic rendering is implemented. Similarly, a literature review of monoscopic rendering of rain and snow is completed to learn about the behavior and distribution of particles in precipitation phenomena. From these reviews, it is hypothesized that the monoscopic rendering of rain or snow can be extended to stereo with real-time and photorealistic results. The goal of this study is to validate this hypothesis and demonstrate it by implementing a particle system using a graphics processing unit (GPU).;The challenges include modeling realistic particle distributions, use of illumination models, and the impact of scene dynamics due to environmental changes. The modern open graphics library shading language (GLSL) and single instruction multiple threads (SIMT) architecture is used to take advantage of data-parallelism in a graphics processor. The particle geometry is modeled by a few vertices, which are morphed into a raindrop or snowflake shapes. Every vertex is processed in parallel, using the SIMT GPU architecture.;A compute shader program, a new compute mode GPU programming language, is used to implement the effects of physical forces on rain or snow particles. Additionally for rain, the concept of retinal persistence is used to elongate the raindrop so that it appears as a falling rain streak. Dynamic level of detail on rain streaks and snowflakes is implemented so that particles closer to the viewer have more visual detail then particles farther away. Illumination models are applied for photorealistic output. The scene is rendered for the leftand right-eye views to produce stereoscopic output, while reducing rendering complexity by drawing some features such as object shadows only once.;Additional experiments are performed to evaluate and compare various 2D-3D software video converters. The goal of these experiments is to determine effectiveness of the 2D-3D converters in producing realistic stereoscopic output of scenes containing water phenomenon. Such scenes are challenging to convert due to scene complexity such as details in scene dynamics, illumination, and reflective distortion. Comparisons between five 2D-3D software video converters are provided by using quantitative and subjective evaluations. The study concludes with experiments on the visual factors necessary to produce photorealistic output. The experimental method uses a series of controlled human experiments where participants are presented with video clips and still photographs of real precipitation. The stimuli vary along three visual factors such as number of particles, particle sizes, and their motion. The goal is to determine the statistical ranking and importance of these visual factors for producing a photorealistic output. The experiments are extended to investigate if stereo improves photorealism. Experimental stimuli include post-processing on rendered output to produce variable lighting, glow, and fog effects to study their impact on photorealism as the stereo camera moves in the scene.