Photogrammetric Solution for Analysis of Out-Of-Plane Movements of a Masonry Structure in a Large-Scale Laboratory Experiment

Abstract

This paper proposes a photogrammetric procedure able to determine out-of-plane movements experienced by a masonry structure subjected to a quasi-static cyclic test. The method tracks the movement of circular targets by means of a coarse-to-fine strategy. These targets were captured by means of a photogrammetric network, made up of four cameras optimized following the precepts of a zero-, first-, and second-order design. The centroid of each circular target was accurately detected for each image using the Hough transform, a sub-pixel edge detector based on the partial area effect, and a non-linear square optimization strategy. The three-dimensional (3D) coordinates of these targets were then computed through a photogrammetric bundle adjustment considering a self-calibration model of the camera. To validate the photogrammetric method, measurements were carried out in parallel to an ongoing test on a full-scale two-story unreinforced masonry structure (5.4 × 5.2 × 5.4-m) monitored with more than 200 contact sensors. The results provided by the contact sensors during one of the load phases were compared with those obtained by the proposed approach. According to this accuracy assessment, the method was able to determine the out-of-plane displacement during the quasi-static cyclic test with a sub-pixel accuracy of 0.58. evaluated, and, thus, requires the use of registration strategies (with introduce an additional error source) to place them into a common coordinate system [1]. In addition to this, its measurement principle-based on the emission and reception of a laser beam-within the necessity of having a dense point cloud, requires the investment of several minutes to capture the whole scene. This issue restricts the use of this technology to those cases in which the structure is completely static [3,9,13,18,19].Another potential approach for the analysis of changes and deformation in structures that does not share this restriction is photogrammetry [4,[6][7][8][10][11][12]14,15,17,[20][21][22]. This approach, in contrast to laser scanning, is relatively low-cost as it is possible to obtain reliable results by means of common digital single-lens reflex (DSLR) cameras [6,15,16,21,22]. In addition to this, its flexibility makes it possible to evaluate the deformation suffered by different engineering solutions, from small scales (e.g., mechanical tests) [16,[21][22][23]] to large structures [7,14,15,20]. This property of the ability to capture several images per second makes it possible to use this technology in dynamic scenarios (e.g., shaking table tests) [7,14,17,20,[24][25][26][27]. Within this discipline, there are three strategies that are commonly applied in order to evaluate the changes that occur during a scenario: (i) digital image correlation method (DIC) [10][11][12]16]; (ii) structure from motion approach using change detection algorithms (i.e., cloud-to-cloud comparison algorithms) [15,[28][29][30]; and (iii) point-tracking approaches [14,20,23,25,26,31]. While the first two methods are able to produce f...

Novel Pole Photogrammetric System for Low-Cost Documentation of Archaeological Sites: The Case Study of “Cueva Pintada”

“…These binary targets also helped to scale the photogrammetric model. Particularly, the center of these targets was extracted following the approach developed in [29]. This approach extracts accurately the centroid of each circular target using the Hough transform, a sub-pixel edge detector based on the partial area effect, and a non-linear square optimization strategy.…”

High-Speed Videogrammetry with Mutually Guided Target Tracking under Occlusion for Masonry Building Structure Displacement on a Shaking Table

“…The natural targets usually disappear completely when they are occluded, making it impossible to obtain continuous displacement. To obtain the continuous displacement response under occlusion, the artificial targets which disappear partially are usually pasted on the surface of the interested key location of the tested objects [20][21][22][23][24]. The ellipse target is widely used as one type of artificial target in photogrammetry and computer vision, because it is characterized by geometric and rotational invariance.…”