Browsing by Subject "Structure from motion"
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Item Advanced techniques for centimeter-accurate GNSS positioning on low-cost mobile platforms(2015-12) Pesyna, Kenneth Mark Jr.; Humphreys, Todd Edwin; Heath, Robert W., Ph. D.; Vikalo, Haris; York, Johnathan; Sanghavi, SujayOver the past decade, GPS and other Global Navigation Satellite System (GNSS) chipsets have become smaller, cheaper, and more energy efficient, so much so that they now come standard in most smartphones and tablets. Under good multipath conditions, one can expect 2-to-3-meter-accurate positioning with these chipsets, under adverse multipath, accuracy degrades to 10 meters or worse. Outside the mainstream of consumer GNSS receivers, however, centimeter---even millimeter---accurate GNSS receivers are used routinely in geodesy, agriculture, and surveying. The key to their accuracy is a radically different approach to positioning in which the standard code-phase (or pseudorange) positioning technique is replaced by differential carrier-phase positioning. Adopting this high-precision carrier-phase-based technique for consumer-grade mobile devices is possible, but comes with significant challenges. This dissertation identifies and addresses the challenges to performing centimeter accurate carrier-phase differential GNSS (CDGNSS) positioning on low-cost mobile devices. To this end, this dissertation makes three primary contributions. First, this dissertation develops a carrier phase reconstruction technique to address the high power consumption of current CDGNSS algorithms. The reconstruction technique enables a continuous and unambiguous phase time history to be reconstructed from intermittent phase measurements, permitting aggressive duty cycling of the mobile device's internal GNSS chip, decreasing energy consumption. Second, this dissertation demonstrates that a centimeter-accurate positioning solution is possible based on GNSS data collected using a smartphone, a first in the open literature. It is identified that the primary impediment to performing CDGNSS on smartphones lies not in the commodity GNSS chipset within the phone, but instead in the antenna, whose chief failing is its poor multipath suppression, resulting in long initialization times. It is demonstrated that wavelength-scale random antenna motion can be used to decorrelate multipath errors and reduce the initialization period---the so-called time-to-ambiguity-resolution (TAR)---of smartphones employing CDGNSS to obtain centimeter-level positioning fix. Finally, this dissertation develops a framework that tightly fuses smartphone camera image measurements with GNSS carrier phase measurements to reduce CDGNSS initialization times beyond what is achievable using antenna motion alone. The framework augments the traditional bundle-adjustment- (BA-)-based structure from motion (SFM) algorithm with the carrier phase differential GNSS (CDGNSS) algorithm in a way that preserves the key features of both algorithms, namely the sparseness of the matrices in BA and the integer structure of the ambiguities in CDGNSS. The framework is shown to produce a faster, more robust, and more accurate positioning solution than achievable with existing techniques.Item Analysis of independent motion detection in 3D scenes(2012-08) Floren, Andrew William; Bovik, Alan C. (Alan Conrad), 1958-In this thesis, we develop an algorithm for detecting independent motion in real-time from 2D image sequences of arbitrarily complex 3D scenes. We discuss the necessary background information in image formation, optical flow, multiple view geometry, robust estimation, and real-time camera and scene pose estimation for constructing and understanding the operation of our algorithm. Furthermore, we provide an overview of existing independent motion detection techniques and compare them to our proposed solution. Unfortunately, the existing independent motion detection techniques were not evaluated quantitatively nor were their source code made publicly available. Therefore, it is not possible to make direct comparisons. Instead, we constructed several comparison algorithms which should have comparable performance to these previous approaches. We developed methods for quantitatively comparing independent motion detection algorithms and found that our solution had the best performance. By establishing a method for quantitatively evaluating these algorithms and publishing our results, we hope to foster better research in this area and help future investigators more quickly advance the state of the art.