Terrestrial laser scanner (TLS) is a non-contact sensor, optics-based instrument that collects three dimensional (3D) data of a defined region of an object surface automatically and in a systematic pattern with a high data collecting rate. This capability has made TLS widely applied for numerous 3D applications. With the ability to provide dense 3D data, TLS has improved the processing phase in constructing complete 3D model, which is much simpler and faster. Pre-processing is one of the phases involved, which consisted of registration and georeferencing procedures. Due to the many error sources occur in TLS measurement, thus, pre-processing can be considered as very crucial phase to identify any existence of errors and outliers. Any presence of errors in this phase can decrease the quality of TLS final product. With intention to discuss about this issue, this study has performed two experiments, which involved with data collection for land slide monitoring and 3D topography. By implementing both direct and indirect pre-processing method, the outcomes have indicated that TLS is suitable for applications which require centimetre level of accuracy.
ABSTRACT:Nowadays, terrestrial laser scanning shows the potential to improve construction productivity by measuring the objects changes using realtime applications. This paper presents the process of implementation of an efficient framework for precast concrete using terrestrial laser scanning that enables contractors to acquire accurate data and support Quality Assessment System in Construction (QLASSIC). Leica Scanstation C10, black/white target, Autodesk Revit and Cyclone software were used in this study. The results were compared with the dimensional of based model precast concrete given by the company as a reference with the AutoDesk Revit model from the terrestrial laser scanning data and conventional method (measuring tape). To support QLASSIC, the tolerance dimensions of cast in-situ & precast elements is +10mm / -5mm. The results showed that the root mean square error for a Revit model is 2.972mm while using measuring tape is 13.687mm. The accuracy showed that terrestrial laser scanning has an advantage in construction jobs to support QLASSIC.
The ability to provide rapid and dense three-dimensional (3D) data have made many 3D applications easier. However, similar to other optical and electronic instruments, data from TLS can also be impaired with errors. Self-calibration is a method available to investigate those errors in TLS observations which has been adopted from photogrammetry technique. Though, the network configuration applied by both TLS and photogrammetry techniques are quite different. Thus, further investigation is required to verify whether the photogrammetry principal regarding datum constraints selection is applicable to TLS self-calibration. To ensure that the assessment is thoroughly done, the datum constraints analyses were carried out using three variant network configurations: 1) minimum number of scan stations, 2) minimum number of surfaces for targets distribution, and 3) minimum number of point targets. Via graphical and statistical, the analyses of datum constraints selection have indicated that the parameter correlations obtained are significantly similar.
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