Automatic Planning for Scanning: Optimizing 3D Laser Scanning Operations Using BIM and TLS

摘要

Application of Terrestrial Laser Scanning (TLS) technology in the Architectural Engineering and Construction (AEC) industry is gaining popularity because the technology uniquely offers the means to create as-built three dimensional (3D) models of existing facilities, and conduct construction project progress and dimensional quality measurements. An open challenge with regard to the use TLS for such applications is to efficiently generate effective scanning plans that satisfy pre-defined point cloud quality specifications. Two such specifications are currently commonly used: Level of Accuracy (LOA) that focuses on individual point precision, and Level of Detail (LOD) that focuses on point density. Given such specifications, current practice sees professionals manually prepare scanning plans using existing 2D CAD drawings, some ad-hoc rules (of thumb), and their experience. However, LOA and LOD are point-based specifications, and do not ensure that a sufficient amount of the surface of each object is covered by the acquired data, despite this being important to many of the applications for which TLS is employed (e.g. modelling existing facilities). Therefore, this research uniquely proposes a novel planning for scanning specification, called Level of Surface Completeness (LOC) that assesses point cloud quality in terms of surface acquisition completeness. In addition, an approach is proposed for automatic planning for scanning in the AEC industry that takes both LOA and LOC specifications into account. The approach is 'generic' in the sense that it can be employed for any type of project It is designed to generate automatic laser scanning plans using as input: (1) the facility's 3D BIM model; (2) the scanner's characteristics; and (3) the LOA and LOC specifications. The output is the smallest (optimal) set of scanning locations necessary to achieve those requirements. The results are evaluated in terms of effectiveness, efficiency and sensitivity analysis. However, the experimental results also highlight a significant issue of the approach which is that it does not take into account the overlapping of surfaces covered from different scanning locations.