A Virtual Testbed for Fish-Tank Virtual Reality: Improving Calibration with a Virtual-in-Virtual Display

With the development of novel calibration techniques for multimedia projectors and curved projection surfaces, volumetric 3D displays are becoming easier and more affordable to build. The basic requirements include a display shape that defines the volume (e.g. a sphere, cylinder, or cuboid) and a tracking system to provide each user's location for the perspective corrected rendering. When coupled with modern graphics cards, these displays are capable of high resolution, low latency, high frame rate, and even stereoscopic rendering; however, like many previous studies have shown, every component must be precisely calibrated for a compelling 3D effect. While human perceptual requirements have been extensively studied for head-tracked displays, most studies featured seated users in front of a flat display. It remains unclear if results from these flat display studies are applicable to newer, walk-around displays with enclosed or curved shapes. To investigate these issues, we developed a virtual testbed for volumetric head-tracked displays that can measure calibration accuracy of the entire system in real-time. We used this testbed to investigate visual distortions of prototype curved displays, improve existing calibration techniques, study the importance of stereo to performance and perception, and validate perceptual calibration with novice users. Our experiments show that stereo is important for task performance, but requires more accurate calibration, and that novice users can make effective use of perceptual calibration tools. We also propose a novel, real-time calibration method that can be used to fine-tune an existing calibration using perceptual feedback. The findings from this work can be used to build better head-tracked volumetric displays with an unprecedented amount of 3D realism and intuitive calibration tools for novice users

Contributions to virtual reality

153 p.The thesis contributes in three Virtual Reality areas: ¿ Visual perception: a calibration algorithm is proposed to estimate stereo projection parameters in head-mounted displays, so that correct shapes and distances can be perceived, and calibration and control procedures are proposed to obtain desired accommodation stimuli at different virtual distances.¿ Immersive scenarios: the thesis analyzes several use cases demanding varying degrees of immersion and special, innovative visualization solutions are proposed to fulfil their requirements. Contributions focus on machinery simulators, weather radar volumetric visualization and manual arc welding simulation.¿ Ubiquitous visualization: contributions are presented to scenarios where users access interactive 3D applications remotely. The thesis follows the evolution of Web3D standards and technologies to propose original visualization solutions for volume rendering of weather radar data, e-learning on energy efficiency, virtual e-commerce and visual product configurators

THE UNIVERSAL MEDIA BOOK

We explore the integration of projected imagery with a physical book that acts as a tangible interface to multimedia data. Using a camera and projector pair, a tracking framework is presented wherein the 3D position of planar pages are monitored as they are turned back and forth by a user, and data is correctly warped and projected onto each page at interactive rates to provide the user with an intuitive mixed-reality experience. The book pages are blank, so traditional camera-based approaches to tracking physical features on the display surface do not apply. Instead, in each frame, feature points are independently extracted from the camera and projector images, and matched to recover the geometry of the pages in motion. The book can be loaded with multimedia content, including images and videos. In addition, volumetric datasets can be explored by removing a page from the book and using it as a tool to navigate through a virtual 3D volume

HOLOGRAPHICS: Combining Holograms with Interactive Computer Graphics

Among all imaging techniques that have been invented throughout the last decades, computer graphics is one of the most successful tools today. Many areas in science, entertainment, education, and engineering would be unimaginable without the aid of 2D or 3D computer graphics. The reason for this success story might be its interactivity, which is an important property that is still not provided efficiently by competing technologies – such as holography. While optical holography and digital holography are limited to presenting a non-interactive content, electroholography or computer generated holograms (CGH) facilitate the computer-based generation and display of holograms at interactive rates [2,3,29,30]. Holographic fringes can be computed by either rendering multiple perspective images, then combining them into a stereogram [4], or simulating the optical interference and calculating the interference pattern [5]. Once computed, such a system dynamically visualizes the fringes with a holographic display. Since creating an electrohologram requires processing, transmitting, and storing a massive amount of data, today’s computer technology still sets the limits for electroholography. To overcome some of these performance issues, advanced reduction and compression methods have been developed that create truly interactive electroholograms. Unfortunately, most of these holograms are relatively small, low resolution, and cover only a small color spectrum. However, recent advances in consumer graphics hardware may reveal potential acceleration possibilities that can overcome these limitations [6]. In parallel to the development of computer graphics and despite their non-interactivity, optical and digital holography have created new fields, including interferometry, copy protection, data storage, holographic optical elements, and display holograms. Especially display holography has conquered several application domains. Museum exhibits often use optical holograms because they can present 3D objects with almost no loss in visual quality. In contrast to most stereoscopic or autostereoscopic graphics displays, holographic images can provide all depth cues—perspective, binocular disparity, motion parallax, convergence, and accommodation—and theoretically can be viewed simultaneously from an unlimited number of positions. Displaying artifacts virtually removes the need to build physical replicas of the original objects. In addition, optical holograms can be used to make engineering, medical, dental, archaeological, and other recordings—for teaching, training, experimentation and documentation. Archaeologists, for example, use optical holograms to archive and investigate ancient artifacts [7,8]. Scientists can use hologram copies to perform their research without having access to the original artifacts or settling for inaccurate replicas. Optical holograms can store a massive amount of information on a thin holographic emulsion. This technology can record and reconstruct a 3D scene with almost no loss in quality. Natural color holographic silver halide emulsion with grain sizes of 8nm is today’s state-of-the-art [14]. Today, computer graphics and raster displays offer a megapixel resolution and the interactive rendering of megabytes of data. Optical holograms, however, provide a terapixel resolution and are able to present an information content in the range of terabytes in real-time. Both are dimensions that will not be reached by computer graphics and conventional displays within the next years – even if Moore’s law proves to hold in future. Obviously, one has to make a decision between interactivity and quality when choosing a display technology for a particular application. While some applications require high visual realism and real-time presentation (that cannot be provided by computer graphics), others depend on user interaction (which is not possible with optical and digital holograms). Consequently, holography and computer graphics are being used as tools to solve individual research, engineering, and presentation problems within several domains. Up until today, however, these tools have been applied separately. The intention of the project which is summarized in this chapter is to combine both technologies to create a powerful tool for science, industry and education. This has been referred to as HoloGraphics. Several possibilities have been investigated that allow merging computer generated graphics and holograms [1]. The goal is to combine the advantages of conventional holograms (i.e. extremely high visual quality and realism, support for all depth queues and for multiple observers at no computational cost, space efficiency, etc.) with the advantages of today’s computer graphics capabilities (i.e. interactivity, real-time rendering, simulation and animation, stereoscopic and autostereoscopic presentation, etc.). The results of these investigations are presented in this chapter

A Modular and Open-Source Framework for Virtual Reality Visualisation and Interaction in Bioimaging

Life science today involves computational analysis of a large amount and variety of data, such as volumetric data acquired by state-of-the-art microscopes, or mesh data from analysis of such data or simulations. The advent of new imaging technologies, such as lightsheet microscopy, has resulted in the users being confronted with an ever-growing amount of data, with even terabytes of imaging data created within a day. With the possibility of gentler and more high-performance imaging, the spatiotemporal complexity of the model systems or processes of interest is increasing as well. Visualisation is often the first step in making sense of this data, and a crucial part of building and debugging analysis pipelines. It is therefore important that visualisations can be quickly prototyped, as well as developed or embedded into full applications. In order to better judge spatiotemporal relationships, immersive hardware, such as Virtual or Augmented Reality (VR/AR) headsets and associated controllers are becoming invaluable tools. In this work we present scenery, a modular and extensible visualisation framework for the Java VM that can handle mesh and large volumetric data, containing multiple views, timepoints, and color channels. scenery is free and open-source software, works on all major platforms, and uses the Vulkan or OpenGL rendering APIs. We introduce scenery's main features, and discuss its use with VR/AR hardware and in distributed rendering. In addition to the visualisation framework, we present a series of case studies, where scenery can provide tangible benefit in developmental and systems biology: With Bionic Tracking, we demonstrate a new technique for tracking cells in 4D volumetric datasets via tracking eye gaze in a virtual reality headset, with the potential to speed up manual tracking tasks by an order of magnitude. We further introduce ideas to move towards virtual reality-based laser ablation and perform a user study in order to gain insight into performance, acceptance and issues when performing ablation tasks with virtual reality hardware in fast developing specimen. To tame the amount of data originating from state-of-the-art volumetric microscopes, we present ideas how to render the highly-efficient Adaptive Particle Representation, and finally, we present sciview, an ImageJ2/Fiji plugin making the features of scenery available to a wider audience.:Abstract Foreword and Acknowledgements Overview and Contributions Part 1 - Introduction 1 Fluorescence Microscopy 2 Introduction to Visual Processing 3 A Short Introduction to Cross Reality 4 Eye Tracking and Gaze-based Interaction Part 2 - VR and AR for System Biology 5 scenery — VR/AR for Systems Biology 6 Rendering 7 Input Handling and Integration of External Hardware 8 Distributed Rendering 9 Miscellaneous Subsystems 10 Future Development Directions Part III - Case Studies C A S E S T U D I E S 11 Bionic Tracking: Using Eye Tracking for Cell Tracking 12 Towards Interactive Virtual Reality Laser Ablation 13 Rendering the Adaptive Particle Representation 14 sciview — Integrating scenery into ImageJ2 & Fiji Part IV - Conclusion 15 Conclusions and Outlook Backmatter & Appendices A Questionnaire for VR Ablation User Study B Full Correlations in VR Ablation Questionnaire C Questionnaire for Bionic Tracking User Study List of Tables List of Figures Bibliography Selbstständigkeitserklärun

Calibration Methods for Head-Tracked 3D Displays

Head-tracked 3D displays can provide a compelling 3D effect, but even small inaccuracies in the calibration of the participant’s viewpoint to the display can disrupt the 3D illusion. We propose a novel interactive procedure for a participant to easily and accurately calibrate a head-tracked display by visually aligning patterns across a multi-screen display. Head-tracker measurements are then calibrated to these known viewpoints. We conducted a user study to evaluate the effectiveness of different visual patterns and different display shapes. We found that the easiest to align shape was the spherical display and the best calibration pattern was the combination of circles and lines. We performed a quantitative camera-based calibration of a cubic display and found visual calibration outperformed manual tuning and generated viewpoint calibrations accurate to within a degree. Our work removes the usual, burdensome step of manual calibration when using head-tracked displays and paves the way for wider adoption of this inexpensive and effective 3D display technology