Shadow mapping algorithms: Applications and limitations

This study provides an overview of popular and famous algorithms and techniques in shadow maps generation.Well- known techniques in shadow maps generation is described detail, along with a discussion of the advantages and drawbacks of each. Basic ideas, improvements and future works of the techniques are also comprehensively summarized and analyzed in depth. Often, programmers have difficulty selecting an appropriate shadow generation algorithm that is specific to their purpose. We have classified and systemized these techniques. The main goal of this paper is to provide researchers with background on a variety of shadow mapping techniques so as make it easier for them to choose the method best suited to their aims. It is al-so hoped that our analysis will help researchers find solutions to the shortcomings of each technique. © 2015 NSP Natural Sciences Publishing Co

Robust object-based algorithms for direct shadow simulation

En informatique graphique, les algorithmes de générations d'ombres évaluent la quantité de lumière directement perçue par une environnement virtuel. Calculer précisément des ombres est cependant coûteux en temps de calcul. Dans cette dissertation, nous présentons un nouveau système basé objet robuste, qui permet de calculer des ombres réalistes sur des scènes dynamiques et ce en temps interactif. Nos contributions incluent notamment le développement de nouveaux algorithmes de génération d'ombres douces ainsi que leur mise en oeuvre efficace sur processeur graphique. Nous commençons par formaliser la problématique du calcul d'ombres directes. Tout d'abord, nous définissons ce que sont les ombres directes dans le contexte général du transport de la lumière. Nous étudions ensuite les techniques interactives qui génèrent des ombres directes. Suite à cette étude nous montrons que mêmes les algorithmes dit physiquement réalistes se reposent sur des approximations. Nous mettons également en avant, que malgré leur contraintes géométriques, les algorithmes d'ombres basées objet sont un bon point de départ pour résoudre notre problématique de génération efficace et robuste d'ombres directes. Basé sur cette observation, nous étudions alors le système basé objet existant et mettons en avant ses problèmes de robustesse. Nous proposons une nouvelle technique qui améliore la qualité des ombres générées par ce système en lui ajoutant une étape de mélange de pénombres. Malgré des propriétés et des résultats convaincants, les limitations théoriques et de mise en oeuvre limite la qualité générale et les performances de cet algorithme. Nous présentons ensuite un nouvel algorithme d'ombres basées objet. Cet algorithme combine l'efficacité de l'approche basée objet temps réel avec la précision de sa généralisation au rendu hors ligne. Notre algorithme repose sur l'évaluation locale du nombre d'objets entre deux points : la complexité de profondeur. Nous décrivons comment nous utilisons cet algorithme pour échantillonner la complexité de profondeur entre les surfaces visibles d'une scène et une source lumineuse. Nous générons ensuite des ombres à partir de cette information soit en modulant l'éclairage direct soit en intégrant numériquement l'équation d'illumination directe. Nous proposons ensuite une extension de notre algorithme afin qu'il puisse prendre en compte les ombres projetées par des objets semi-opaque. Finalement, nous présentons une mise en oeuvre efficace de notre système qui démontre que des ombres basées objet peuvent être générées de façon efficace et ce même sur une scène dynamique. En rendu temps réel, il est commun de représenter des objets très détaillés encombinant peu de triangles avec des textures qui représentent l'opacité binaire de l'objet. Les techniques de génération d'ombres basées objet ne traitent pas de tels triangles dit "perforés". De par leur nature, elles manipulent uniquement les géométries explicitement représentées par des primitives géométriques. Nous présentons une nouvel algorithme basé objet qui lève cette limitation. Nous soulignons que notre méthode peut être efficacement combinée avec les systèmes existants afin de proposer un système unifié basé objet qui génère des ombres à la fois pour des maillages classiques et des géométries perforées. La mise en oeuvre proposée montre finalement qu'une telle combinaison fournit une solution élégante, efficace et robuste à la problématique générale de l'éclairage direct et ce aussi bien pour des applications temps réel que des applications sensibles à la la précision du résultat.Direct shadow algorithms generate shadows by simulating the direct lighting interaction in a virtual environment. The main challenge with the accurate direct shadow problematic is its computational cost. In this dissertation, we develop a new robust object-based shadow framework that provides realistic shadows at interactive frame rate on dynamic scenes. Our contributions include new robust object-based soft shadow algorithms and efficient interactive implementations. We start, by formalizing the direct shadow problematic. Following the light transport problematic, we first formalize what are robust direct shadows. We then study existing interactive direct shadow techniques and outline that the real time direct shadow simulation remains an open problem. We show that even the so called physically plausible soft shadow algorithms still rely on approximations. Nevertheless we exhibit that, despite their geometric constraints, object-based approaches seems well suited when targeting accurate solutions. Starting from the previous analyze, we investigate the existing object-based shadow framework and discuss about its robustness issues. We propose a new technique that drastically improve the resulting shadow quality by improving this framework with a penumbra blending stage. We present a practical implementation of this approach. From the obtained results, we outline that, despite desirable properties, the inherent theoretical and implementation limitations reduce the overall quality and performances of the proposed algorithm. We then present a new object-based soft shadow algorithm. It merges the efficiency of the real time object-based shadows with the accuracy of its offline generalization. The proposed algorithm lies onto a new local evaluation of the number of occluders between $two$ points (\ie{} the depth complexity). We describe how we use this algorithm to sample the depth complexity between any visible receiver and the light source. From this information, we compute shadows by either modulate the direct lighting or numerically solve the direct illumination with an accuracy depending on the light sampling strategy. We then propose an extension of our algorithm in order to handle shadows cast by semi opaque occluders. We finally present an efficient implementation of this framework that demonstrates that object-based shadows can be efficiently used on complex dynamic environments. In real time rendering, it is common to represent highly detailed objects with few triangles and transmittance textures that encode their binary opacity. Object-based techniques do not handle such perforated triangles. Due to their nature, they can only evaluate the shadows cast by models whose their shape is explicitly defined by geometric primitives. We describe a new robust object-based algorithm that addresses this main limitation. We outline that this method can be efficiently combine with object-based frameworks in order to evaluate approximative shadows or simulate the direct illumination for both common meshes and perforated triangles. The proposed implementation shows that such combination provides a very strong and efficient direct lighting framework, well suited to many domains ranging from quality sensitive to performance critical applications

Shadow Rendering Using View Frustum Splitting Methods in OpenGL

Tato práce pojednává o generování kaskádových stínových map ve 3D aplikacích. Popisuje dvě vybrané metody dělení pohledového tělesa na tyto kaskády a rozebírá jejich rozdílnosti. Pro analýzu byla vyvinuta aplikace za použití rozhraní OpenGL, která na třech scénách ukazuje výhody a nevýhody těchto metod. Práce se zaměřila na porovnání vykreslování každé kaskády zvlášť a pomocí vícevrstvých textur pro shadow mapy. Analýza dat prokázala některé výhody vrstového vykreslování. Metoda PSSM byla dle analýzy rychlejší, ovšem metoda SDSM na druhou stranu produkovala lepší výsledky.The content of this thesis discusses the generation of cascaded shadow maps in 3D applications. It describes two chosen methods of view frustum splitting into sub-frustum and discusses their differences. It was developed an application for analysation purposes in OpenGL which shows their advantages and disadvantages on three testing scenes. This work is focused on a comparison of drawing each split separately and using layered rendering. Data analysis proved some advantages of layered rendering. The PSSM was faster in accord to data analysis, but SDSM, on the other hand, produces more accurate shadows.

Logarithmic perspective shadow maps

The shadow map algorithm is a popular approach for generating shadows for real-time applications. Shadow maps are flexible and easy to implement, but they are prone to aliasing artifacts. To reduce aliasing artifacts we introduce logarithmic perspective shadow maps (LogPSMs). LogPSMs are based on a novel shadow map parameterization that consists of a perspective projection and a logarithmic transformation. They can be used for both point and directional light sources to produce hard shadows. To establish the benefits of LogPSMs, we perform an in-depth analysis of shadow map aliasing error and the error characteristics of existing algorithms. Using this analysis we compute a parameterization that produces near-optimal perspective aliasing error. This parameterization has high arithmetical complexity which makes it less practical than existing methods. We show, however, that over all light positions, the simpler LogPSM parameterization produces the same maximum error as the near-optimal parameterization. We also show that compared with competing algorithms, LogPSMs produce significantly less aliasing error. Equivalently, for the same error as competing algorithms, LogPSMs require significantly less storage and bandwidth. We demonstrate difference in shadow quality achieved with LogPSMs on several models of varying complexity. LogPSMs are rendered using logarithmic rasterization. We show how current GPU architectures can be modified incrementally to perform logarithmic rasterization at current GPU fill rates. Specifically, we modify the rasterizer to support rendering to a nonuniform grid with the same watertight rasterization properties as current rasterizers. We also describe a novel depth compression scheme to handle the nonlinear primitives produced by logarithmic rasterization. Our proposed architecture enhancements align with current trends of decreasing cost for on-chip computation relative to off-chip bandwidth and storage. For only a modest increase in computation, logarithmic rasterization can greatly reduce shadow map bandwidth and storage costs

Realistic Visualization of Animated Virtual Cloth

Photo-realistic rendering of real-world objects is a broad research area with applications in various different areas, such as computer generated films, entertainment, e-commerce and so on. Within photo-realistic rendering, the rendering of cloth is a subarea which involves many important aspects, ranging from material surface reflection properties and macroscopic self-shadowing to animation sequence generation and compression. In this thesis, besides an introduction to the topic plus a broad overview of related work, different methods to handle major aspects of cloth rendering are described. Material surface reflection properties play an important part to reproduce the look & feel of materials, that is, to identify a material only by looking at it. The BTF (bidirectional texture function), as a function of viewing and illumination direction, is an appropriate representation of reflection properties. It captures effects caused by the mesostructure of a surface, like roughness, self-shadowing, occlusion, inter-reflections, subsurface scattering and color bleeding. Unfortunately a BTF data set of a material consists of hundreds to thousands of images, which exceeds current memory size of personal computers by far. This work describes the first usable method to efficiently compress and decompress a BTF data for rendering at interactive to real-time frame rates. It is based on PCA (principal component analysis) of the BTF data set. While preserving the important visual aspects of the BTF, the achieved compression rates allow the storage of several different data sets in main memory of consumer hardware, while maintaining a high rendering quality. Correct handling of complex illumination conditions plays another key role for the realistic appearance of cloth. Therefore, an upgrade of the BTF compression and rendering algorithm is described, which allows the support of distant direct HDR (high-dynamic-range) illumination stored in environment maps. To further enhance the appearance, macroscopic self-shadowing has to be taken into account. For the visualization of folds and the life-like 3D impression, these kind of shadows are absolutely necessary. This work describes two methods to compute these shadows. The first is seamlessly integrated into the illumination part of the rendering algorithm and optimized for static meshes. Furthermore, another method is proposed, which allows the handling of dynamic objects. It uses hardware-accelerated occlusion queries for the visibility determination. In contrast to other algorithms, the presented algorithm, despite its simplicity, is fast and produces less artifacts than other methods. As a plus, it incorporates changeable distant direct high-dynamic-range illumination. The human perception system is the main target of any computer graphics application and can also be treated as part of the rendering pipeline. Therefore, optimization of the rendering itself can be achieved by analyzing human perception of certain visual aspects in the image. As a part of this thesis, an experiment is introduced that evaluates human shadow perception to speedup shadow rendering and provides optimization approaches. Another subarea of cloth visualization in computer graphics is the animation of the cloth and avatars for presentations. This work also describes two new methods for automatic generation and compression of animation sequences. The first method to generate completely new, customizable animation sequences, is based on the concept of finding similarities in animation frames of a given basis sequence. Identifying these similarities allows jumps within the basis sequence to generate endless new sequences. Transmission of any animated 3D data over bandwidth-limited channels, like extended networks or to less powerful clients requires efficient compression schemes. The second method included in this thesis in the animation field is a geometry data compression scheme. Similar to the BTF compression, it uses PCA in combination with clustering algorithms to segment similar moving parts of the animated objects to achieve high compression rates in combination with a very exact reconstruction quality.Realistische Visualisierung von animierter virtueller Kleidung Das photorealistisches Rendering realer Gegenstände ist ein weites Forschungsfeld und hat Anwendungen in vielen Bereichen. Dazu zählen Computer generierte Filme (CGI), die Unterhaltungsindustrie und E-Commerce. Innerhalb dieses Forschungsbereiches ist das Rendern von photorealistischer Kleidung ein wichtiger Bestandteil. Hier reichen die wichtigen Aspekte, die es zu berücksichtigen gilt, von optischen Materialeigenschaften über makroskopische Selbstabschattung bis zur Animationsgenerierung und -kompression. In dieser Arbeit wird, neben der Einführung in das Thema, ein weiter Überblick über ähnlich gelagerte Arbeiten gegeben. Der Schwerpunkt der Arbeit liegt auf den wichtigen Aspekten der virtuellen Kleidungsvisualisierung, die oben beschrieben wurden. Die optischen Reflektionseigenschaften von Materialoberflächen spielen eine wichtige Rolle, um das so genannte look & feel von Materialien zu charakterisieren. Hierbei kann ein Material vom Nutzer identifiziert werden, ohne dass er es direkt anfassen muss. Die BTF (bidirektionale Texturfunktion)ist eine Funktion die abhängig von der Blick- und Beleuchtungsrichtung ist. Daher ist sie eine angemessene Repräsentation von Reflektionseigenschaften. Sie enthält Effekte wie Rauheit, Selbstabschattungen, Verdeckungen, Interreflektionen, Streuung und Farbbluten, die durch die Mesostruktur der Oberfläche hervorgerufen werden. Leider besteht ein BTF Datensatz eines Materials aus hunderten oder tausenden von Bildern und sprengt damit herkömmliche Hauptspeicher in Computern bei weitem. Diese Arbeit beschreibt die erste praktikable Methode, um BTF Daten effizient zu komprimieren, zu speichern und für Echtzeitanwendungen zum Visualisieren wieder zu dekomprimieren. Die Methode basiert auf der Principal Component Analysis (PCA), die Daten nach Signifikanz ordnet. Während die PCA die entscheidenen visuellen Aspekte der BTF erhält, können mit ihrer Hilfe Kompressionsraten erzielt werden, die es erlauben mehrere BTF Materialien im Hauptspeicher eines Consumer PC zu verwalten. Dies erlaubt ein High-Quality Rendering. Korrektes Verwenden von komplexen Beleuchtungssituationen spielt eine weitere, wichtige Rolle, um Kleidung realistisch erscheinen zu lassen. Daher wird zudem eine Erweiterung des BTF Kompressions- und Renderingalgorithmuses erläutert, die den Einsatz von High-Dynamic Range (HDR) Beleuchtung erlaubt, die in environment maps gespeichert wird. Um die realistische Erscheinung der Kleidung weiter zu unterstützen, muss die makroskopische Selbstabschattung integriert werden. Für die Visualisierung von Falten und den lebensechten 3D Eindruck ist diese Art von Schatten absolut notwendig. Diese Arbeit beschreibt daher auch zwei Methoden, diese Schatten schnell und effizient zu berechnen. Die erste ist nahtlos in den Beleuchtungspart des obigen BTF Renderingalgorithmuses integriert und für statische Geometrien optimiert. Die zweite Methode behandelt dynamische Objekte. Dazu werden hardwarebeschleunigte Occlusion Queries verwendet, um die Sichtbarkeitsberechnung durchzuführen. Diese Methode ist einerseits simpel und leicht zu implementieren, anderseits ist sie schnell und produziert weniger Artefakte, als vergleichbare Methoden. Zusätzlich ist die Verwendung von veränderbarer, entfernter HDR Beleuchtung integriert. Das menschliche Wahrnehmungssystem ist das eigentliche Ziel jeglicher Anwendung in der Computergrafik und kann daher selbst als Teil einer erweiterten Rendering Pipeline gesehen werden. Daher kann das Rendering selbst optimiert werden, wenn man die menschliche Wahrnehmung verschiedener visueller Aspekte der berechneten Bilder analysiert. Teil der vorliegenden Arbeit ist die Beschreibung eines Experimentes, das menschliche Schattenwahrnehmung untersucht, um das Rendern der Schatten zu beschleunigen. Ein weiteres Teilgebiet der Kleidungsvisualisierung in der Computergrafik ist die Animation der Kleidung und von Avataren für Präsentationen. Diese Arbeit beschreibt zwei neue Methoden auf diesem Teilgebiet. Einmal ein Algorithmus, der für die automatische Generierung neuer Animationssequenzen verwendet werden kann und zum anderen einen Kompressionsalgorithmus für eben diese Sequenzen. Die automatische Generierung von völlig neuen, anpassbaren Animationen basiert auf dem Konzept der Ähnlichkeitssuche. Hierbei werden die einzelnen Schritte von gegebenen Basisanimationen auf Ähnlichkeiten hin untersucht, die zum Beispiel die Geschwindigkeiten einzelner Objektteile sein können. Die Identifizierung dieser Ähnlichkeiten erlaubt dann Sprünge innerhalb der Basissequenz, die dazu benutzt werden können, endlose, neue Sequenzen zu erzeugen. Die Übertragung von animierten 3D Daten über bandbreitenlimitierte Kanäle wie ausgedehnte Netzwerke, Mobilfunk oder zu sogenannten thin clients erfordert eine effiziente Komprimierung. Die zweite, in dieser Arbeit vorgestellte Methode, ist ein Kompressionsschema für Geometriedaten. Ähnlich wie bei der Kompression von BTF Daten wird die PCA in Verbindung mit Clustering benutzt, um die animierte Geometrie zu analysieren und in sich ähnlich bewegende Teile zu segmentieren. Diese erkannten Segmente lassen sich dann hoch komprimieren. Der Algorithmus arbeitet automatisch und erlaubt zudem eine sehr exakte Rekonstruktionsqualität nach der Dekomprimierung

Adaptive Reuse of Surface Parking Lots for Winter-City Streetscape Improvement: A Case Study of Saskatoon, SK

In winter-cities such as Saskatoon there exists a significant potential to improve cold-weather walking conditions for most pedestrians. To realize the walkability potential of a winter-city downtown, by necessity automobile traffic must be reduced. However, when surface parking lots are permitted to operate in abundance, isolated and uncoordinated, and detached from overall planning and transportation policy, automobile traffic reduction downtown cannot be efficiently achieved. In many winter-cities, Saskatoon included, downtown parking lots in fact are oversupplied. Vital space for housing, employment and public space is thereby reduced and pedestrian winter exposure to wind chill and sidewalk ice is increased by breaks in the urban fabric. Systematic conversion of surface parking lots into mixed use would not only enhance incentives to walk, but simultaneously would reduce the incentive to drive. The question thus arises whether and how can we screen a large number of surface parking lots for a limited number of candidate-sites that could be earmarked for infill redevelopment. A screening methodology that prioritizes potential parking lot sites ought to account for a wide range of criteria that address urban design, development-potential, proximity, and microclimate. In a case study of parking lots in downtown Saskatoon, a screening methodology has yielded one priority site out of an inventory of twenty-four sites. Integrated within public transit policy the proposed methodology has generic applicability to downtown areas elsewhere, and can advance the goal of safety and higher residential density downtown

Art (that) works: design guidelines for equitable public art

Master of Landscape ArchitectureDepartment of Landscape Architecture/Regional and Community PlanningMajor Professor Not ListedPublic art within a public space should be experienced by all people (Hein 2006; Phillips 1989; Zebracki 2013). However, when attitudinal, organizational or systemic, and architectural or physical barriers exist, the experience of public art may exclude Persons with Disabilities (Council of Ontario Universities 2013; Schaffer 2020). When people are unable to equitably experience public art, they are also excluded from cultural communities and artistic interpretations of society. If artists and designers do not know how to purposefully accommodate the experiential needs of diverse audiences, including Persons with Disabilities, public art may not be equitably experienced by all people. While some guidelines exist for equitable art in private settings, such as museums, there is a lack of knowledge about how to create and site equitable public art in public spaces. Thus, to fill this knowledge gap, this project developed design guidelines for artists, designers, and creatives when creating and siting equitable public art in public space. The guidelines consider the needs of “all” people to include mobility (physical disabilities), cognition (intellectual disabilities and/or neurodiversity), hearing (D/deaf and Hard of Hearing), and vision (B/blind and Low Vision) disabilities. Notably, the graphic design of the guidelines adheres to established graphic design standards for accessibility. Methods used to inform the development of the guidelines included interviews with artists and site designers, and precedent analysis of multi-sensory art and universally-design sites. To demonstrate how the guidelines can be used, a projective art and site design was developed with site analysis and documented through memoing. Findings reveal that for public art to be equitably experienced by all people, it must be both physically accessible and multi-sensory, to engage two or more senses (Barnes 2003; National Recreation and Parks Association 2015; Robinson 1998). Additionally, and most importantly, findings indicate that the most essential component of equitable public art is social. Public art needs to foster social interaction, which can occur when the art is interactive and “comes alive” with engagement (Papalia 2022). By considering the needs of Persons with Disabilities, artists, designers, and creatives have an opportunity to make a more enriching art experience for all people- an experience that all people may not have had otherwise

Identity in city form : the politics of building height

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1995.Includes bibliographical references (197-203).by Weng-Huat Chew.M.C.P