Auto-Calibration and Three-Dimensional Reconstruction for Zooming Cameras

This dissertation proposes new algorithms to recover the calibration parameters and 3D structure of a scene, using 2D images taken by uncalibrated stationary zooming cameras. This is a common configuration, usually encountered in surveillance camera networks, stereo camera systems, and event monitoring vision systems. This problem is known as camera auto-calibration (also called self-calibration) and the motivation behind this work is to obtain the Euclidean three-dimensional reconstruction and metric measurements of the scene, using only the captured images. Under this configuration, the problem of auto-calibrating zooming cameras differs from the classical auto-calibration problem of a moving camera in two major aspects. First, the camera intrinsic parameters are changing due to zooming. Second, because cameras are stationary in our case, using classical motion constraints, such as a pure translation for example, is not possible. In order to simplify the non-linear complexity of this problem, i.e., auto-calibration of zooming cameras, we have followed a geometric stratification approach. In particular, we have taken advantage of the movement of the camera center, that results from the zooming process, to locate the plane at infinity and, consequently to obtain an affine reconstruction. Then, using the assumption that typical cameras have rectangular or square pixels, the calculation of the camera intrinsic parameters have become possible, leading to the recovery of the Euclidean 3D structure. Being linear, the proposed algorithms were easily extended to the case of an arbitrary number of images and cameras. Furthermore, we have devised a sufficient constraint for detecting scene parallel planes, a useful information for solving other computer vision problems

Robust pan/tilt compensation for foreground-background segmentation

In this paper, we describe a robust method for compensating the panning and tilting motion of a camera, applied to foreground-background segmentation. First, the necessary internal camera parameters are determined through feature-point extraction and tracking. From these parameters, two motion models for points in the image plane are established. The first model assumes a fixed tilt angle, whereas the second model allows simultaneous pan and tilt. At runtime, these models are used to compensate for the motion of the camera in the background model. We will show that these methods provide a robust compensation mechanism and improve the foreground masks of an otherwise state-of-the-art unsupervised foreground-background segmentation method. The resulting algorithm is always able to obtain F1 scores above 80% on every daytime video in our test set when a minimal number of only eight feature matches are used to determine the background compensation, whereas the standard approaches need significantly more feature matches to produce similar results

A Photogrammetry-Based Hybrid System for Dynamic Tracking and Measurement

Noncontact measurements of lightweight flexible aerospace structures present several challenges. Objects are usually mounted on a test stand because current noncontact measurement techniques require that the net motion of the object be zero. However, it is often desirable to take measurements of the object under operational conditions, and in the case of miniature aerial vehicles (MAVs) and deploying space structures, the test article will undergo significant translational motion. This thesis describes a hybrid noncontact measurement system which will enable measurement of structural kinematics of an object freely moving about a volume. By using a real-time videogrammetry system, a set of pan-tilt-zoom (PTZ) cameras is coordinated to track large-scale net motion and produce high-speed, high-quality images for photogrammetric surface reconstruction. The design of the system is presented in detail. A method of generating the calibration parameters for the PTZ cameras is presented and evaluated and is shown to produce good results. The results of camera synchronization tests and tracking accuracy evaluation are presented as well. Finally, a demonstration of the hybrid system is presented in which all four PTZ cameras track an MAV in flight

3D object reconstruction using computer vision : reconstruction and characterization applications for external human anatomical structures

Tese de doutoramento. Engenharia Informática. Faculdade de Engenharia. Universidade do Porto. 201

Scalable multi-view stereo camera array for real world real-time image capture and three-dimensional displays

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2004.Includes bibliographical references (leaves 71-75).The number of three-dimensional displays available is escalating and yet the capturing devices for multiple view content are focused on either single camera precision rigs that are limited to stationary objects or the use of synthetically created animations. In this work we will use the existence of inexpensive digital CMOS cameras to explore a multi- image capture paradigm and the gathering of real world real-time data of active and static scenes. The capturing system can be developed and employed for a wide range of applications such as portrait-based images for multi-view facial recognition systems, hypostereo surgical training systems, and stereo surveillance by unmanned aerial vehicles. The system will be adaptable to capturing the correct stereo views based on the environmental scene and the desired three-dimensional display. Several issues explored by the system will include image calibration, geometric correction, the possibility of object tracking, and transfer of the array technology into other image capturing systems. These features provide the user more freedom to interact with their specific 3-D content while allowing the computer to take on the difficult role of stereoscopic cinematographer.Samuel L. Hill.S.M

Imaging for stereoscopic displays.

This thesis addresses the problem of calibrating a stereoscopic camera with a minimum of necessary post-processing. This is achieved through a two step procedure, the first step of which is a calibration of the sensors in rotation by means of laser diffraction, without attached lenses. The second step involves attaching the lenses and using a simplified conventional image-based calibration to determine the effects of motions of the optical centres due to lens focusing. Mounting considerations and long-term stability are also addressed. This method enables the construction of a stereoscopic camera which requires no interpolative rectification, with the calibration maintaining accuracy over a range of focal distances. Such a camera is built and calibrated, and tested to demonstrate the validity of the predicted error estimates. This approach is shown to be effective in producing stereoscopic images for display which meet the requirements of the human visual system. A comparison of this approach with previously published methods is presented. Some or all of the techniques described in this thesis may be incorporated into existing calibration schemes to improve the quality of the produced stereoscopic images. The improvements provided by a hardware calibration as described may be especially valuable in applications where maintaining full sensor resolution in the displayed image is desired

High-Precision Photogrammetry for Glaciology

Consumer-grade digital cameras have become ubiquitous tools for documenting short-term variability in the geosciences. However, these devices were not intended for precise timekeeping and surveying, and their use as such requires management of systematic and random errors that inevitably arise.This dissertation presents a suite of methods for registering the place and time of photographs in an absolute reference frame so that they may be analyzed and interpreted alongside other spatial and temporal data. The methods are tested on a 13-year record of 33,000 time-lapse photographs from Alaska's Columbia Glacier. This work provides insights into the capabilities and shortcomings of consumer-grade cameras as scientific instruments, the opportunistic approaches often needed to achieve the best results, and the potential of continuous high-frequency measurements for documenting rapid geomorphic processes.Subsecond-precision image capture times are achieved by measuring the offset to a reference clock display and accounting for the drift, precision, and reporting resolution of the camera clock. Two case studies illustrate the benefit of subsecond precision in contemporary investigations: georeferencing aerial photogrammetric surveys with camera positions time-interpolated from GPS tracklogs, and coupling videos of glacier-calving events to synchronous seismic waveforms. Retroactive dating of photographs, on the order of seconds to hours, is achieved by leveraging phenomena visible in the photographs -- namely, the positions of astronomical objects in the sky or the corresponding variations in solar radiation and sea level.Similarly, retroactive camera calibrations are achieved using surface and topographic features in the photographs -- specifically, point and line features of known absolute position, the motion of static features in images due to camera rotation, and the correspondences between real images and images synthesized from vertical imagery. Camera motion is corrected by computing globally optimal estimates of rotation over arbitrarily-long photographic sequences.Finally, a recently-developed tracking algorithm based on particle filtering theory is refined and applied to estimate Columbia Glacier velocities, their associated uncertainties, and the corresponding strain rate fields at 3-day intervals over a 13-year period, providing an unprecedented look at the seasonal and sub-seasonal variability of tidewater glacier dynamics over long time scales

Modeling and Simulation in Engineering

This book provides an open platform to establish and share knowledge developed by scholars, scientists, and engineers from all over the world, about various applications of the modeling and simulation in the design process of products, in various engineering fields. The book consists of 12 chapters arranged in two sections (3D Modeling and Virtual Prototyping), reflecting the multidimensionality of applications related to modeling and simulation. Some of the most recent modeling and simulation techniques, as well as some of the most accurate and sophisticated software in treating complex systems, are applied. All the original contributions in this book are jointed by the basic principle of a successful modeling and simulation process: as complex as necessary, and as simple as possible. The idea is to manipulate the simplifying assumptions in a way that reduces the complexity of the model (in order to make a real-time simulation), but without altering the precision of the results

Manufacturing Metrology

Metrology is the science of measurement, which can be divided into three overlapping activities: (1) the definition of units of measurement, (2) the realization of units of measurement, and (3) the traceability of measurement units. Manufacturing metrology originally implicates the measurement of components and inputs for a manufacturing process to assure they are within specification requirements. It can also be extended to indicate the performance measurement of manufacturing equipment. This Special Issue covers papers revealing novel measurement methodologies and instrumentations for manufacturing metrology from the conventional industry to the frontier of the advanced hi-tech industry. Twenty-five papers are included in this Special Issue. These published papers can be categorized into four main groups, as follows: Length measurement: covering new designs, from micro/nanogap measurement with laser triangulation sensors and laser interferometers to very-long-distance, newly developed mode-locked femtosecond lasers. Surface profile and form measurements: covering technologies with new confocal sensors and imagine sensors: in situ and on-machine measurements. Angle measurements: these include a new 2D precision level design, a review of angle measurement with mode-locked femtosecond lasers, and multi-axis machine tool squareness measurement. Other laboratory systems: these include a water cooling temperature control system and a computer-aided inspection framework for CMM performance evaluation