Abstract
Dense point clouds acquired from Terrestrial Laser Scanners (TLS) have proved to be effective for structural deformation assessment. In the last decade, many researchers have defined methodology and workflow in order to compare different point clouds, with respect to each other or to a known model, assessing the potentialities and limits of this technique. Currently, dense point clouds can be obtained by Close-Range Photogrammetry (CRP) based on a Structure from Motion (SfM) algorithm. This work reports on a comparison between the TLS technique and the Close-Range Photogrammetry using the Structure from Motion algorithm. The analysis of two Reinforced Concrete (RC) beams tested under four-points bending loading is presented. In order to measure displacement distributions, point clouds at different beam loading states were acquired and compared. A description of the instrumentation used and the experimental environment, along with a comprehensive report on the calculations and results obtained is reported. Two kinds of point clouds comparison were investigated: Mesh to mesh and modeling with geometric primitives. The comparison between the mesh to mesh (m2m) approach and the modeling (m) one showed that the latter leads to significantly better results for both TLS and CRP. The results obtained with the TLS for both m2m and m methodologies present a Root Mean Square (RMS) levels below 1 mm, while the CRP method yields to an RMS level of a few millimeters for m2m, and of 1 mm for m.
Highlights
Structural Health Monitoring is one of the main objectives of engineering surveys [1] and it is important for buildings, bridges, dams, or other infrastructures subjected to extreme events such as earthquakes, hurricane, flooding, fire [2,3], or due to natural aging [4,5]
Methodologies Comparison In order to evaluate the accuracy of Terrestrial Laser Scanners (TLS) and Close-Range Photogrammetry (CRP), the displacements estimated with these methods were compared with the ones obtained from the Laser Tracker (LT) and DPA
The goal of this research was to investigate the obtainable accuracy in the structural displacement measurements with CRP based on the Structure from Motion algorithm, and to compare this with the TLS technique
Summary
Structural Health Monitoring is one of the main objectives of engineering surveys [1] and it is important for buildings, bridges, dams, or other infrastructures subjected to extreme events such as earthquakes, hurricane, flooding, fire [2,3], or due to natural aging [4,5]. The main target of this research was to evaluate the accuracy and precision that can be obtained by CRP point clouds measuring structural deformations. Measurement techniques and data processing of the structural deformations are shown, and a comparison between the TLS technique and the CRP is presented. The second has a nominal measurement accuracy of 2 μm + 5 μm/m (RMS), or 3 μm + 7 μm/m (3σ) Both systems obtain the coordinates of targeted points with a very high precision and all the comparisons between the examined techniques (TLS and CRP) have been performed with respect to those targets. Methodologies Comparison In order to evaluate the accuracy of TLS and CRP, the displacements estimated with these methods were compared with the ones obtained from the LT and DPA. For the sake of simplicity, on, the accuracy of TLS and CRP will be evaluated only versus DPA
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