Development of a calibration pipeline for a monocular-view structured illumination 3D sensor utilizing an array projector

Commercial off-the-shelf digital projection systems are commonly used in active structured illumination photogrammetry of macro-scale surfaces due to their relatively low cost, accessibility, and ease of use. They can be described as inverse pinhole modelled. The calibration pipeline of a 3D sensor utilizing pinhole devices in a projector-camera setup configuration is already well-established. Recently, there have been advances in creating projection systems offering projection speeds greater than that available from conventional off-the-shelf digital projectors. However, they cannot be calibrated using well established techniques based on the pinole assumption. They are chip-less and without projection lens. This work is based on the utilization of unconventional projection systems known as array projectors which contain not one but multiple projection channels that project a temporal sequence of illumination patterns. None of the channels implement a digital projection chip or a projection lens. To workaround the calibration problem, previous realizations of a 3D sensor based on an array projector required a stereo-camera setup. Triangulation took place between the two pinhole modelled cameras instead. However, a monocular setup is desired as a single camera configuration results in decreased cost, weight, and form-factor. This study presents a novel calibration pipeline that realizes a single camera setup. A generalized intrinsic calibration process without model assumptions was developed that directly samples the illumination frustum of each array projection channel. An extrinsic calibration process was then created that determines the pose of the single camera through a downhill simplex optimization initialized by particle swarm. Lastly, a method to store the intrinsic calibration with the aid of an easily realizable calibration jig was developed for re-use in arbitrary measurement camera positions so that intrinsic calibration does not have to be repeated

Model-based asymptotically optimal dispersion measure correction for pulsar timing

In order to reach the sensitivity required to detect gravitational waves, pulsar timing array experiments need to mitigate as much noise as possible in timing data. A dominant amount of noise is likely due to variations in the dispersion measure. To correct for such variations, we develop a statistical method inspired by the maximum likelihood estimator and optimal filtering. Our method consists of two major steps. First, the spectral index and amplitude of dispersion measure variations are measured via a time-domain spectral analysis. Second, the linear optimal filter is constructed based on the model parameters found in the first step, and is used to extract the dispersion measure variation waveforms. Compared to current existing methods, this method has better time resolution for the study of short timescale dispersion variations, and generally produces smaller errors in waveform estimations. This method can process irregularly sampled data without any interpolation because of its time-domain nature. Furthermore, it offers the possibility to interpolate or extrapolate the waveform estimation to regions where no data is available. Examples using simulated data sets are included for demonstration.Comment: 15 pages, 15 figures, submitted 15th Sept. 2013, accepted 2nd April 2014 by MNRAS. MNRAS, 201

Configurable Input Devices for 3D Interaction using Optical Tracking

Three-dimensional interaction with virtual objects is one of the aspects that needs to be addressed in order to increase the usability and usefulness of virtual reality. Human beings have difficulties understanding 3D spatial relationships and manipulating 3D user interfaces, which require the control of multiple degrees of freedom simultaneously. Conventional interaction paradigms known from the desktop computer, such as the use of interaction devices as the mouse and keyboard, may be insufficient or even inappropriate for 3D spatial interaction tasks. The aim of the research in this thesis is to develop the technology required to improve 3D user interaction. This can be accomplished by allowing interaction devices to be constructed such that their use is apparent from their structure, and by enabling efficient development of new input devices for 3D interaction. The driving vision in this thesis is that for effective and natural direct 3D interaction the structure of an interaction device should be specifically tuned to the interaction task. Two aspects play an important role in this vision. First, interaction devices should be structured such that interaction techniques are as direct and transparent as possible. Interaction techniques define the mapping between interaction task parameters and the degrees of freedom of interaction devices. Second, the underlying technology should enable developers to rapidly construct and evaluate new interaction devices. The thesis is organized as follows. In Chapter 2, a review of the optical tracking field is given. The tracking pipeline is discussed, existing methods are reviewed, and improvement opportunities are identified. In Chapters 3 and 4 the focus is on the development of optical tracking techniques of rigid objects. The goal of the tracking method presented in Chapter 3 is to reduce the occlusion problem. The method exploits projection invariant properties of line pencil markers, and the fact that line features only need to be partially visible. In Chapter 4, the aim is to develop a tracking system that supports devices of arbitrary shapes, and allows for rapid development of new interaction devices. The method is based on subgraph isomorphism to identify point clouds. To support the development of new devices in the virtual environment an automatic model estimation method is used. Chapter 5 provides an analysis of three optical tracking systems based on different principles. The first system is based on an optimization procedure that matches the 3D device model points to the 2D data points that are detected in the camera images. The other systems are the tracking methods as discussed in Chapters 3 and 4. In Chapter 6 an analysis of various filtering and prediction methods is given. These techniques can be used to make the tracking system more robust against noise, and to reduce the latency problem. Chapter 7 focusses on optical tracking of composite input devices, i.e., input devices 197 198 Summary that consist of multiple rigid parts that can have combinations of rotational and translational degrees of freedom with respect to each other. Techniques are developed to automatically generate a 3D model of a segmented input device from motion data, and to use this model to track the device. In Chapter 8, the presented techniques are combined to create a configurable input device, which supports direct and natural co-located interaction. In this chapter, the goal of the thesis is realized. The device can be configured such that its structure reflects the parameters of the interaction task. In Chapter 9, the configurable interaction device is used to study the influence of spatial device structure with respect to the interaction task at hand. The driving vision of this thesis, that the spatial structure of an interaction device should match that of the task, is analyzed and evaluated by performing a user study. The concepts and techniques developed in this thesis allow researchers to rapidly construct and apply new interaction devices for 3D interaction in virtual environments. Devices can be constructed such that their spatial structure reflects the 3D parameters of the interaction task at hand. The interaction technique then becomes a transparent one-to-one mapping that directly mediates the functions of the device to the task. The developed configurable interaction devices can be used to construct intuitive spatial interfaces, and allow researchers to rapidly evaluate new device configurations and to efficiently perform studies on the relation between the spatial structure of devices and the interaction task

Search methods for an autonomous underwater vehicle using scalar measurements

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution July 1996The continuing development of the autonomous underwater vehicle as an oceanographic research tool has opened up the realm of scientific possibility in the field of deep ocean research. The ability of a vehicle to travel to the ocean floor untethered, collect data for an extended period of time and return to the surface for recovery can make precise oceanographic surveying more economically practical and more efficient. This thesis investigates several scalar parameter searching techniques which have their basis in mathematical optimization algorithms and their applicability for use specifically within the context of autonomous underwater vehicle dynamics. In particular, a modified version of the circular gradient evaluation in the simulated environment of a hydrothermal plume is examined as a test case. Using a priori knowledge of the expected structure of the scalar parameter contour is shown to be advantageous in optimizing the search

Articulated patient model in high-precision radiation therapy

In modern high precision radiotherapy, changes in the anatomy of the patient over the course of treatment pose a major challenge. An accurate assessment of occurring anatomical variations is the key requirement to enable an adaptation of the treatment plan for ensuring a highly precise treatment. Comparison of commonly used deformable image registration shows large discrepancies regarding the quality of anatomical alignment, benchmarked on a common data pool. One of the main reasons is found in widely used transformation models, insufficiently reflecting the actual deformation behaviour of the underlying tissue. Thus, especially in the highly heterogeneous head and neck area, which is characterized by many organs at risk being in proximity to the tumor as well as posture changes induced by the interplay of several bones, an accurate assessment of anatomical changes is essential for a successful adaptive radiotherapy. A physically meaningful transformation model offering a high biofidelity is required to provide an accurate anatomical alignment in such area. In this work, a novel biomechanical deformation model based on kinematics and multi-body physics for the whole head and neck area is introduced to guarantee the representation of physically meaningful transformations. The developed kinematic model is individually tailored to each patient as it is based on the delineated bones extracted from the computer tomography scan. It encompasses all bones relevant for head and neck cancer treatment, including bones of the proximal upper extremities, the shoulder girdle, cranial region, the rib cage and the vertebral column. Moreover, the model is designed to be easily extendible to other body regions. All bones are connected by ball and socket joints, which are automatically localized based on their individual geometries. A kinematic graph maintains the hierarchy of the connected bones across the whole skeleton to enable the propagation of local transformations to other body regions by inverse kinematics. Accuracy, robustness and computational efficiency of the kinematic model were retrospectively evaluated on patient datasets representative for typical inter-fractional variations as well as separately acquired image scans with large arms-up to arms-down posture changes. Using landmarks defined by multiple observers as reference, the overall mean accuracy of the kinematic model in reproducing postures in the image scans was found to be around 1 millimetre, which is settled slightly above the inter-observer variation. In detail, the assessed accuracy revealed potential for improvement regarding the automated positioning of the intervertebral joints in the region of the cervical spine. Due to the complex shape of the vertebrae, a relocation of the joint rotation centres towards the line connecting the centres of the intervertebral disks seems beneficial. Moreover, the use of ball and socket joints for the acromioclavicular joints has shown to be insufficient for mimicking the large arms-up to arms-down posture change due to the lack of representing translational offsets, observed in the image scans. The strong regularization of the permissible deformations in the skeletal anatomy leads to a higher robustness against conflicting input such as flawed or mixed-up anatomical feature points. Furthermore, such a physical-object-oriented transformation model requires even less input to describe meaningful deformations. With the total degrees of freedom of the kinematic head and neck model limited to those specified by the joints, the computation of new arbitrary skeletal postures is achieved within less than 50 milliseconds. With such efficient computation on the one hand and the strong regularization of deformations on the other hand, the kinematic model seems suitable for its application in a registration approach. In addition, it was demonstrated how the kinematic model can be successfully embedded into a registration approach as a transformation model to enable the fully automatic extraction of anatomical variations from image scans. This was accomplished by coupling the model to an extended simplex downhill optimizer and an overlap based similarity metric. The anatomy of pre-selected bones is aligned following a hierarchical optimization scheme. In conclusion, the novel developed kinematic model guarantees a deformation modelling of high biofidelity and efficiency, thus promising an assessment of anatomical changes without the need of an extensive visual inspection of the results as otherwise expected. To date, successful application of adaptive radiotherapy especially for tumors in regions characterized by a high anatomical flexibility is hampered by a lacking reliability of conventional deformation models. While associated uncertainties can be compensated at the cost of extended safety margins for photon therapy, prevailing range uncertainties when using particles currently impede the treatment of tumors in such areas. The dissemination of the proposed kinematic deformation model into the clinics provides a way to lay the foundation towards broadening the spectrum of patients eligible for treatment with particles, carried out at the increasing number of particle therapy centres worldwide

Tools for discovering and characterizing extrasolar planets

Among the group of extrasolar planets, transiting planets provide a great opportunity to obtain direct measurements for the basic physical properties, such as mass and radius of these objects. These planets are therefore highly important in the understanding of the evolution and formation of planetary systems: from the observations of photometric transits, the interior structure of the planet and atmospheric properties can also be constrained. The most efficient way to search for transiting extrasolar planets is based on wide-field surveys by hunting for short and shallow periodic dips in light curves covering quite long time intervals. These surveys monitor fields with several degrees in diameter and tens or hundreds of thousands of objects simultaneously. In the practice of astronomical observations, surveys of large field-of-view are rather new and therefore require special methods for photometric data reduction that have not been used before. In this PhD thesis, I summarize my efforts related to the development of a complete software solution for high precision photometric reduction of astronomical images. I also demonstrate the role of this newly developed package and the related algorithms in the case of particular discoveries of the HATNet project. [abridged]Comment: PhD thesis, Eotvos Lorand University (June 18, 2009), 68 pages in journal style, 41 figures, 18 table