Risk assessment: a comparison between the use of laser scanners and total stations in a situation where time is the critical factor

For some time past, terrestrial laser scanning has been adopted as one of the data acquisition techniques for e.g. deformation measurements, documentation of historical monuments and civil engineering projects. Using terrestrial laser scanning, millions of 3D points can be obtained with a high accuracy in a time span of minutes or even seconds depending on the type of laser scanner. However, processing the data still remains a time consuming process. As a result, total station measurements are often preferred over laser scanning for high frequency deformation measurements when time for data processing is limited. In the research at hand, the applicability of terrestrial laser scanning in time critical situations was assessed based on the case of a recent monitoring project on a sewage purification plant. Deformations had to be assessed twice a day in order to prevent accidents from happening. The total station measurements were executed and processed by a specialized company (Teccon bvba, Belgium). At the same time, terrestrial laser scanning was used by researchers of University College Ghent and Ghent University to acquire deformation data. The data obtained by laser scanning was processed independently and then georeferenced to the same coordinate system as used for the total station measurements to enable comparison of the resulting deformations. In order to be able to meet the time requirements, a “quick and dirty” method was developed to process the laser scan data. This method implied no cleaning up of the point clouds and only primitive modeling of parts of the structure. Although a complete 3D model of the whole structure could not be generated in the limited time frame between two scans, the objective, namely an accurate assessment of deformations almost in real time, was accomplished. Furthermore, the degree of detail that can be reached through the use of laser scanning surpasses the possibilities of total stations. Moreover, even with a “quick and dirty method”, visualization is much more comprehensive than can be obtained by using a total station