College of Engineering Theses and Dissertations
Permanent URI for this collectionhttps://hdl.handle.net/1969.6/94188
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Browsing College of Engineering Theses and Dissertations by Author "Chu, Tianxing"
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Item Constructing a digital land record system(2019-08) Gillis, Bryan S.; Smith, Richard; Chu, Tianxing; Rudowsky, Catherine; Tissot, PhilippeLand records represent the legal bindings of a person to their property and assist in the execution of property ownership. Protecting these documents and adopting a clear system to manage them should be a priority to every private citizen with interest in real property in the United States. Unfortunately, existing land record systems have become dated and fail to protect land records and offer little-to-no transparency or accessibility. Fortunately, more modern digital land record systems are being developed to combat these issues. When constructing a digital land record system, it is necessary to (1) identify the economic and functional value of using digital land record systems for a government entity, (2) establish procedures for the digitization of physical land record systems, and (3) provide digital land record system examples that meet the base needs of a land administration system with public access that follows both geospatial data and digital library standards. This thesis evaluates the needs of a successful digital land record system and outlines the development and capabilities of BandoCat, a modern digital land record system project at the Conrad Blucher Institute for Surveying and Science (CBI) at Texas A&M University – Corpus Christi. This thesis will assess the current state of land record systems in the United States and highlight the current inefficiencies and issues existing in these systems, thereby necessitating the development of BandoCat as a modern solution. The design of modern land record systems is founded in the standards of digital libraries. These digital libraries serve as long-term data stewards and provide well-developed standards which land record systems can leverage. This thesis details the parameters of BandoCat, how it leverages digital library standards, its modern features (such as georectification and adherence to metadata standards), and how modern land record systems (such as BandoCat) address current digital land record systems’ shortcomings, facilitate easier access for stakeholders, easier system interoperability, and visualization of land records information. It is the hopes of the author that this thesis will serve as a guide to improving the state of land record systems in the United States. Through the combination of the modern digital land record systems, such as BandoCat, with a consistent and interoperable design, the state of land administration can be vastly improved. The procedures and methodology created by the author provide a baseline for improving land record systems, and the BandoCat system developed by the Spatial {Query} Lab provides a software to begin the transition from physical to digital land record systems.Item Evaluation of different GNSS solutions and SFM software workflows for surveying shorelines and remote areas using UAS(2022-05) Pilartes-Congo Jr, José A.; Starek, Michael J.; Chu, Tianxing; Huang, YuxiaThe emergence and modernization of Unoccupied Aircraft Systems (UAS), broadly known as drones, and Structure-from-Motion (SfM) photogrammetry have made significant contributions to the geospatial and surveying world. Traditionally, indirect georeferencing by using ground control points (GCPs) is used to georeference UAS imagery when high accuracy positioning is required. However, this approach is tedious and impractical when surveying remote or inaccessible coastal areas, or when desiring to map coastlines from shipborne UAS operations. The broad applicability of UAS and SfM technologies has led to a wide range of data collection and SfM processing workflows that can be utilized, enhanced further by the implementation of various Global Navigation Satellite Systems (GNSS) techniques for direct georeferencing of the imagery. As part of an investigation conducted by the Office of Coast Survey (OCS) at the National Oceanic and Atmospheric Administration (NOAA), this study seeks to identify UAS-SfM data collection and processing workflows that maintain vertical accuracies at the decimeter-level without the aiding of GCPs. The study uses UAS imagery collected from two different UAS platforms at two different sandy beach study sites along the Southern Texas Gulf Coast. The objectives of the study are two-fold: (i) examine the applicability of Real-Time Kinematic (RTK), Post-Processed Kinematic (PPK), and Precise Point Positioning (PPP) GNSS solutions as plausible substitutes to ground control points (GCPs) for UAS-SfM shoreline mapping, and (ii) to evaluate the impact of three-commercial SfM software (Drone2Map, Metashape, and Pix4D) and one open-source software (Web OpenDroneMap) on the quantitative and qualitative characteristics of resulting mapping products. Results showed that RTK and PPK can reach centimeter-level vertical accuracies, fulfill the requirements set forth for this project, and are the most suitable alternatives to GCPs for remote surveying when plausible. When using PPK, the highest accuracies were reached when using base stations within 30 kilometers of the survey site, especially when combined with higher percentages of PPK fix, a measure that explains the number of photos that successfully underwent PPK correction. PPP offers the best alternative for remote UAS surveying, given that it is a single - receiver method, but the results evaluated here did not meet desired vertical accuracy levels. However, enhancing convergence time techniques is likely to reach even better results. In terms of SfM software, Metashape and Pix4D proved to be the most robust software altern atives achieving repeatable centimeter-level vertical accuracies for derived mapping products. Several inconsistencies were observed with Drone2Map and ODM, which hinder its applicability for UAS surveying without GCPs. The results and techniques discussed in this study help to optimize data acquisition and processing workflows for shoreline mapping and remote surveying.Item Evaluation of environmental impacts produced by gold mining areas on the surrounding forest in southwestern Ecuador using multispectral satellite and uas imagery(2020-08) Veloz, Edison; Starek, Michael J.; Chu, Tianxing; Devlin, DonnaMining is a dangerous activity that can cause environmental damage to flora and fauna due to the utilization of heavy metals. Ecuador has a long history of mineral extractions and nowadays the activity is increasing in many parts of the country. Environmentalists state that chemicals, such as cyanide and mercury, could cause alterations in vegetation health. This study utilizes satellite and Unmanned Aircraft System (UAS) based remote sensing to analyze impacts to vegetation health around a mining area located in Bella Rica within the El Oro province of the southwestern zone of Ecuador. Vegetation can be analyzed and identified through many remote sensing techniques, one of them is the Normalized Difference Vegetation Index (NDVI). This band ratio index ranges from +1 to -1 and uses red and near-infrared (NIR) bands to identify the presence of healthy or stressed vegetation. In this study, a small rotary UAS equipped with a two-band sensor recording red and NIR reflectance and a separate red-green-blue (RGB) digital camera was used to gather data and determine if vegetation closer to the mine exhibited different NDVI patterns compared to vegetation located farther away. Spatial differences in NDVI patterns may indicate potential impacts of waste from mining operations. To provide a time series assessment of vegetation changes around the mine, satellite imagery from PlanetScope was acquired and analyzed to measure changes in NDVI throughout the years 2017, 2018, and 2019. PlanetScope uses an array of miniaturized satellites, called CubeSats, equipped with four-band multispectral sensors providing imagery at a resolution of 3 m ground sample distance (GSD). In comparison, spatial resolution of the UAS products, which is dependent on flying height, range from 2.97 cm GSD for the RGB camera to 11.4 cm GSD for the multispectral sensor. Satellite derived NDVI was vi statistically compared to UAS derived NDVI values to assess the impact of spatial resolution and sensor quality on NDVI measurement. Furthermore, the UAS acquired RGB imagery was processed using Structure from Motion (SfM) photogrammetry to derive a 3D reconstruction of the scene, referred to as a point cloud. Properties of the point cloud data were analyzed to determine if relationships exist between land cover structure and NDVI patterns captured in the UAS multispectral imagery. From UAS based multispectral data, significant differences in NDVI values were found between vegetation close to the mining area and vegetation at longer distances (p < 0.05), indicating that mining waste could be altering NDVI values in the region. Satellite imagery analysis suggests that changes in NDVI are related to different human activities that have been developed inside the study area. UAS derived NDVI shows a strong linear relationship with PlanetScope derived NDVI (R = 0.91), suggesting that the low cost and light-weight sensor onboard the UAS was able to capture similar reflectance information but at much higher resolution. UAS-SfM point cloud data was applied to measure spatial variation in point density and canopy height, and determine if these measures could serve as a proxy for NDVI to assess vegetation health impacts from the mining operation. Results varied with NDVI and point cloud density exhibiting a weak relationship (R = 0.04). This relationship held at multiple resolutions suggesting that scene texture and uniformity in the densification stage of SfM does not correlate well with variation in NDVI due to differences in canopy cover. Interestingly, point cloud density changes did show a connection to the type of vegetation with high values of point density occurring over the more densely canopied forest areas. In contrast to point cloud density, UASSfM derived canopy height measures exhibited much stronger correlation to the UAS multispectral NDVI values (R = 0.69).Item UAS mapping for oil spill response in sandy beach environments: Feasibility and best practices(2021-12) Berryhill, Jacob; Starek, Michael J.; Chu, Tianxing; Gibeaut, JimOil spill events can be catastrophically harmful to coastal ecosystems, causing considerable and long-term environmental and economic impacts before associated consequences are finally eliminated. Conducting timely, flexible, and accurate surveys immediately after a spill incident is of crucial importance for oil spill response in order to locate the spill, determine the size and volume of the spill, monitor and track the oil movement. Traditional survey methods and visual observations are usually performed for investigating the affected shoreline after an oil spill. Field sketches are used to record and convey the state of oiling in the affected areas. Diagnosis of oiling extent is limited to line-of-sight observations on the ground or by expensive manned aircraft operations. Recently, Unmanned Aircraft Systems (UAS) have been increasingly employed in various real-world applications, spanning from military scouting and scientific research to urban planning and entertainment. With the rapid development of miniaturized imaging and positioning technologies, UAS Structure-from-Motion (SfM) photogrammetry has become an emerging, cost-effective, and flexible solution for fulfilling various surveying and mapping needs at local scales. This thesis examined the potential and feasibility of using commercially available rotor copter and fixed-wing UAS platforms with SfM photogrammetric techniques to measure and monitor changes in beach elevation for shoreline oiling surveys. The state of the art of UAS-SfM together with its benefits and generic workflow in oil spill surveying were reviewed. A typical stretch of beach in South Texas was chosen as the study area in the thesis due to abundant historical data collected by the research laboratory from prior projects. The study site contains jetty blocks that provide stable features, as well as beaches that are both maintained and unmaintained. Four objectives were outlined with an effort to develop guidelines for UAS-SfM best practices for Shoreline Cleanup and Assessment Technique (SCAT). Based on the data collected at the study area, research findings suggest that without ground control points (GCPs), SfM processing with post-processing kinematic (PPK)-enabled image locations can achieve remarkably higher accuracy than that with autonomous Global Navigation Satellite System (GNSS) image geotags. Adding more GCPs can exponentially improve the overall accuracy for autonomous GNSS geotagged images. For the specific study area, the accuracy performance of the autonomous GNSS geotagged SfM products is on par with that of the differentially corrected GNSS geotagged SfM products with 10 GCPs used for georeferencing. By comparing against coordinates of the check points, the z residuals of a SfM-generated DSM were found better near the center of the beach and worse towards the water and in the dunes and vegetation. Another benefit of using a rigorous GCP control network is it significantly alleviates the bowling effect. Alternative solution for effectively alleviating the bowling effect in time critical survey missions where surveying GCPs is impossible is the use of high overlap oblique imagery and/or multi-elevation coverage. Height adjustments on erratic height values that occurred within autonomous GNSS geotagged images will not improve the accuracy in DSM rendering, however it is still recommended for reducing time and effort in identifying aerial target locations within the image set. When using the PPK operation mode, special attention needs to be paid because a consistent vertical datum should be maintained for the coordinates of both GCPs and image locations throughout the project. In case rapid SfM processing is considered essential for the sake of time, commercial SfM software demonstrated that several hours may be saved in terms of processing, but overall data quality of the geospatial products may have to be compromised.