Intercomparison among six terrestrial laser scanner systems focused on the measurement of small elements (< 0.5 m) is performed. Phase shift (PS) and time of flight (ToF) scanners are considered. Two standard artefacts containing threedimensional printing spheres and steps of variable height are used for the experiment. Results show errors between -4.5 and 3.5 mm in the measurement of distances between step planes. The most stable systems for measuring small elements seem the Leica C10, Faro Photon and Riegl LMS Z390i. The quality of the results is linked to the overall quality of the system rather than the specific technology used for range measurement (PS or ToF) which does not appear to be a determining factor.

Bricks are the vital component of most masonry structures. Their maintenance is critical to the protection of masonry buildings. Terrestrial Light Detection and Ranging (TLidar) systems provide massive point cloud data in an accurate and fast way. TLidar enables us to sample and store the state of a brick surface in a practical way. This article aims to extract individual bricks from an unorganized pile of bricks sampled by a dense point cloud. The method automatically segments and models the individual bricks. The methodology is divided into five main steps: Filter needless points, brick boundary points removal, coarse segmentation using 3D component analysis, planar segmentation and grouping, and brick reconstruction. A novel voting scheme is used to segment the planar patches in an effective way. Brick reconstruction is based on the geometry of single brick and its corresponding nominal size (length, width and height). The number of bricks reconstructed is around 75%. An accuracy assessment is performed by comparing 3D coordinates of the reconstructed vertices to the manually picked vertices. The standard deviations of differences along x, y and z axes are 4.55 mm, 4.53 mm and 4.60 mm, respectively. The comparison results indicate that the accuracy of reconstruction based on the introduced methodology is high and reliable. The work presented in this paper provides a theoretical basis and reference for large scene applications in brick-like structures. Meanwhile, the high-accuracy brick reconstruction lays the foundation for further brick displacement estimation.

For better understanding how coastal structures with gentle slopes behave during high energy events, a wave attack experiment representing a storm of 3000 waves was performed in a flume facility. Two setups with different steepness of slope were compared under the same conditions. In order to quantify changes in the rock slopes after the wave attack, a terrestrial laser scanner was used to obtain 3D coordinates of the rock surface before and after each experiment. Next, through a series of processing steps, the point clouds were converted to a suitable 2D raster for change analysis. This allowed to estimate detailed and quantitative change information. The results indicate that the area around the artificial coast line, defined as the intersection between sloped surface and wave surface, is most strongly affected by wave attacks. As the distances from the sloped surface to the waves are shorter, changes for the mildly sloped surface, slope 1 (1: 10), are distributed over a larger area compared to the changes for the more steeply sloped surface, slope 2 (1: 5). The results of this experiment show that terrestrial laser scanning is an effective and feasible method for change analysis of rock slopes in a laboratory setting. Most striking results from a process point of view is that the transport direction of the rocks change between the two different slopes: from seaward transport for the steeper slope to landward transport for the milder slope.

A method is introduced for detecting changes from point clouds that avoids registration. For many applications, changes are detected between two scans of the same scene obtained at different times. Traditionally, these scans are aligned to a common coordinate system having the disadvantage that this registration step introduces additional errors. In addition, registration requires stable targets or features. To avoid these issues, we propose a change detection method based on so-called baselines. Baselines connect feature points within one scan. To analyze changes, baselines connecting corresponding points in two scans are compared. As feature points either targets or virtual points corresponding to some reconstructable feature in the scene are used. The new method is implemented on two scans sampling a masonry laboratory building before and after seismic testing, that resulted in damages in the order of several centimeters. The centres of the bricks of the laboratory building are automatically extracted to serve as virtual points. Baselines connecting virtual points and/or target points are extracted and compared with respect to a suitable structural coordinate system. Changes detected from the baseline analysis are compared to a traditional cloud to cloud change analysis demonstrating the potential of the new method for structural analysis.