Browsing by Author "Vitsas, Nick"

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    Photorealistic Simulation and Optimization of Lighting Conditions
    (2024-05) Vitsas, Nick
    Lighting plays a very important role in our everyday life, affecting our safety, comfort, well-being and performance. Today, computational methods and tools can be applied to provide recommendations for improving light conditions and finding energy-efficient ways to exploit natural lighting. This thesis addresses the problem of computational optimization of light transport to improve lighting effectiveness, by improving on various aspects of the process, such as goal-driven parametric geometry configuration for building openings and interior design, efficient natural lighting sampling and interactive photorealistic simulation of light transport. Physically-based light transport is at the core of each task and we show how lighting evaluation has a broader application scope than image synthesis. In the domain of light-driven geometry optimization, the thesis makes two contributions, one concerning the opening design problem and one regarding the optimal arrangement of movable objects for interior design. Opening design comes at the early stages of architectural design. and concerns decisions about the geometric characteristics of windows, skylights, hatches, etc. It greatly impacts the overall energy efficiency, thermal profile, air flow and appearance of a building, both internally and externally. It also directly controls daylighting availability, which is very difficult to predict and assess without automatic tools. We developed a computational methodology and a system to automate the process of opening recommendations in a fully interactive virtual environment, fully supporting parametric constraints and illumination intentions. We optimize openings with respect to their shape, position, size and cardinality, based on Bayesian optimization to propose physically correct openings on the geometry of the building. For the light-driven interior design problem, we proposed and evaluated an automatic interior layout process to produce valid object arrangements guided by geometric and illumination constraints, optimizing for glare, correct illuminance levels and lighting uniformity. Geometric and lighting goals are combined into a cost function that allows for a hierarchical, stochastic exploration of the available space of valid configurations. Optimizing for the contribution of natural lighting is an integral part of any outdoor and indoor environment design process. Analytic formulas for clear skies are a computationally and memory efficient method to create physically accurate sky maps of clear sunny days. However, to simulate light transport, sky models must be efficiently sampled. This is typically done via standard importance sampling approaches for image-based lighting, which tend to be slow and wasteful for the predictable nature of the radiance distribution of analytic sky models. We propose and evaluate a method for fitting a truncated Gaussian mixture model on the radiance distribution of the sky map that is both compact and fast to evaluate. Light-driven geometry optimization requires both accurate and fast light transport evaluation, since a very large number of light-carrying paths needs to be evaluated at each new proposal state. Advances in graphics hardware have enabled interactive ray tracing, which relies on highly optimized data structures for the acceleration of ray queries. Bounding volume hierarchies based on axis-aligned bounding boxes have been the go-to data structure for fast ray-primitive intersections. Similar hierarchies of oriented bounding boxes (OBBs) provide much higher early hierarchy traversal termination rates, however their construction requires complex algorithms for the extraction of tight-fitting OBBs. To further accelerate ray tracing for our tasks, we properly adapt a high quality OBB extraction algorithm from unordered point sets to operate directly on existing hierarchies, to effectively construct an OBB tree on the GPU. By combining our method with existing fast algorithms from the literature that construct hierarchies in real-time, we are able to produce OBB trees that are extremely fast to build and traverse on the GPU. Furthermore, to allow for accurate light transport evaluators accessible as industry-grade tools, we developed and presented WebRays, the first generic ray intersection framework for the Web that offers a programming interface similar to modern ray tracing pipelines for desktop platforms and allows the implementation of light-driven design tools accessible from any platform