Accuracy Analysis of Close-Range Photogrammetry in Civil Engineering Projects

This work involves the study of spatial discrepancies in 3D virtual models generated by commercially available software packages and surveying instruments. Firstly, the software-generated models are produced from sets of multiple 2D overlapping photographic images taken from different locations around the object to be modeled. This technique is now known as Close-Range Photogrammetry and has substantially evolved in the last 30 years, especially for small objects. Secondly, land-surveying equipment is employed to create 3D point-cloud models of the same objects by using a modern laser technology known as Laser Scanning. Proper surveying control is accomplished via accurately established benchmarks around the selected structure(s). The present study focuses on models of relatively large objects, such as topography of construction sites and full civil structures (i.e., houses, buildings, bridges, road intersections, historical structures, etc.). The main objective of this project is to analyze the quality and spatial accuracies obtained in the resulting 3D virtual models. For such purpose, two different popular software packages on close-range photogrammetry, high-resolution cameras, construction-grade total-station instruments and state-of-the-art, 3D laser scanners are available in the recently established Built-Environment and Modeling (BEaM) Lab at the Georgia Southern Civil Engineering and Construction Management Department. This work provides various practical results, including (a) an estimate of the accuracies obtained via close-range photogrammetry; (b) discrepancies between laser scanners and total-station instruments; and (c) the generation of protocols with proper instructions describing the procedures employed in attaining models with minimum errors and certain degree of accuracy. Additionally, two of the participating undergraduate students will use the experience acquired in this project to later produce a virtual 3D model of a Mayan ruin during a study-abroad trip to Merida, Yucatan, Mexico, during the Summer-A term of the 2015 academic year