Optimal Lateral Displacement in Automatic Close-Range Photogrammetry

Abstract

Based on the use of automatic photogrammetry, different researchers made evident that the level of overlap between adjacent photographs directly affects the uncertainty of the 3D dense cloud originated by the Structure from Motion/Image Matching (SfM/IM) process. The purpose of this study was to investigate if, in the case of a convergent shooting typical of close-range photogrammetry, an optimal lateral displacement of the camera for minimizing the 3D data uncertainty could be identified. We examined five different test objects made of rock, differing in terms of stone type and visual appearance. First, an accurate reference data set was generated by acquiring each object with an active range device, based on pattern projection (σz = 18 µm). Then, each object was 3D-captured with photogrammetry, using a set of images taken radially, with the camera pointing to the center of the specimen. The camera–object minimum distance was kept at 200 mm during the shooting, and the angular displacement was as small as π/60. We generated several dense clouds by sampling the original redundant sequence at angular displacements (nπ/60, n=1, 2, … 8). Each 3D cloud was then compared with the reference, implementing an accurate scaling protocol to minimize systematic errors. The residual standard deviation of error made consistently evident a range of angular displacements among images that appear to be optimal for reducing the measurement uncertainty, independent of each specimen shape, material, and texture. Such a result provides guidance about how best to arrange the cameras’ geometry for 3D digitization of a stone cultural heritage artifact with several convergent shots. The photogrammetric tool used in the experiments was Agisoft Metashape.

A low-cost close-range photogrammetric surface scanner

“…Dealing with shiny surfaces was also considered in the approach used by Petruccioli et al (2022), but they utillized an application of matting spray while using conventional turntable photogrammetry in combination with highly controlled illumination. Guidi et al (2020) investigated the relation between the amount of image overlap in the acquisition of photogrammetric data and reconstruction accuracy, leading to the conclusion that a larger overlap is required in close-range photogrammetry (>80%) than that in conventional photogrammetry (40-60%). The experiments performed in this work required a turntable, manual intervention, and incorporating imaging distances of 20 cm.…”

Digital Replicas of British Museum Artefacts

“…On the other hand, to make the entire process truly sustainable, both in the acquisition and processing phases, it is necessary to follow precise control procedures for each step (Farella et al 2022). Since the use of rotating platforms is almost a forced adoption, it is interesting to consider the study of (Guidi et al 2020), which examines the lateral displacement of cameras in typical convergent shooting to assess the influence on the final quality of models. Given the well-known consideration that the ratio between the shooting distance and the baseline of images is much larger in the process supported by SfM compared to traditional photogrammetry, they assessed that values comprised about 5 to 6 minimise the RMS errors.…”

Photogrammetric Method to Determine Physical Aperture and Roughness of a Rock Fracture

“…Other applications of SfM related to rock fracture characterization are prediction of peak shear strength [47], using 3D models obtained by photogrammetry for simulation of fluid flow through a fracture [48], and validation of photogrammetry data with pull and push shear tests to predict friction angle [45,50]. The method was applied successfully for different materials [51][52][53], different sample size [53], and the quality of the reconstructed model was investigated by the angular distance between subsequent images [56]. This efficient and low-cost remote sensing technique generates high-resolution digital 3D models of rock surfaces from a set of images.…”