CONCURRENT LOCALIZATION AND MAPPING WITH SONAR SENSORS AND CONSIDERATION OF VEHICLE MOTION

Simultaneous Localization and Mapping (SLAM) is a procedure used to determine the location of a mobile vehicle in an unknown environment, while constructing a map of the unknown environment at the same time. Mobile platforms, which make use of SLAM algorithms, have industrial applications in autonomous maintenance, such as the inspection of flaws and defects in oil pipelines and storage tanks. A typical SLAM consists of four main components, namely, experimental setup (data gathering), vehicle pose estimation, feature extraction, and filtering. Feature extraction is the process of realizing significant features from the unknown environment such as corners, edges, walls, and interior features. In this work, an original feature extraction algorithm specific to distance measurements obtained through SONAR sensor data is presented. This algorithm has been constructed by combining the SONAR Salient Feature Extraction Algorithm and the Triangulation Hough Based Fusion with point-in-polygon detection. The reconstructed maps obtained through simulations and experimental data with the fusion algorithm are compared to the maps obtained with existing feature extraction algorithms. Based on the results obtained, it is suggested that the proposed algorithm can be employed as an option for data obtained from SONAR sensors in environment, where other forms of sensing are not viable. The algorithm fusion for feature extraction requires the vehicle pose estimation as an input, which is obtained from a vehicle pose estimation model. For the vehicle pose estimation, the author uses sensor integration to estimate the pose of the mobile vehicle. Different combinations of these sensors are studied (e.g., encoder, gyroscope, or encoder and gyroscope). The different sensor fusion techniques for the pose estimation are experimentally studied and compared. The vehicle pose estimation model, which produces the least amount of error, is used to generate inputs for the feature extraction algorithm fusion. In the experimental studies, two different environmental configurations are used, one without interior features and another one with two interior features. Numerical and experimental findings are discussed. Finally, the SLAM algorithm is implemented along with the algorithms for feature extraction and vehicle pose estimation. Three different cases are experimentally studied, with the floor of the environment intentionally altered to induce slipping. Results obtained for implementations with and without SLAM are compared and discussed. The present work represents a step towards the realization of autonomous inspection platforms for performing concurrent localization and mapping in harsh environments.

An Exorbitant Privilege in the First Age of International Financial Integration

The exorbitant privilege literature analyzes the positive differential returns on net foreign assets enjoyed by the United States in the last quarter of the twentieth century as the issuer of the global reserve currency. In the first age of international financial integration (1870-1914), the global reserve currency of the period was the British pound sterling. Whether the United Kingdom enjoyed a similar privilege is analyzed with a new dataset, encompassing microdata on railroad and government financial securities. The use of microdata avoids the flaws that have plagued the US studies, particularly the use of incompatible aggregate variables. New measures of Britain’s net external position provide estimates on capital gains and dividend yields. As the issuer of the global reserve currency, Britain received average revenues of 13.4% of GDP from its international investment position. The country satisfied the necessary condition for the existence of an exorbitant privilege. Nonetheless, Britain’s case is slightly different from the American one. British external assets received higher returns than were paid on external liabilities for each class, but British invested mostly in securities with low profile of risk. The low return on its net external position meant that, for most of the time, Britain would not receive positive revenues from the rest of the world if it were a net debtor country, but this pattern changed after 1900. The finding supports the claim that, at least partially, exorbitant privilege is a general characteristic of the issuer of the global reserve currency and not unique to the late twentieth century US.