Lau Chong Luh

High resolution survey for topographic surveying

In this decade, terrestrial laser scanner (TLS) is getting popular in many fields such as reconstruction, monitoring, surveying, as-built of facilities, archaeology, and topographic surveying. This is due the high speed in data collection which is about 50,000 to 1,000,000 three-dimensional (3D) points per second at high accuracy. The main advantage of 3D representation for the data is that it is more approximate to the real world. Therefore, the aim of this paper is to show the use of High-Definition Surveying (HDS), also known as 3D laser scanning for topographic survey. This research investigates the effectiveness of using terrestrial laser scanning system for topographic survey by carrying out field test in Universiti Teknologi Malaysia (UTM), Skudai, Johor. The 3D laser scanner used in this study is a Leica ScanStation C10. Data acquisition was carried out by applying the traversing method. In this study, the result for the topographic survey is under 1st class survey. At the completion of this study, a standard of procedure was proposed for topographic data acquisition using laser scanning systems. This proposed procedure serves as a guideline for users who wish to utilize laser scanning system in topographic survey fully.

3D Data Fusion Using Unmanned Aerial Vehicle (UAV) Photogrammetry and Terrestrial Laser Scanner (TLS)

Recognizing the various advantages offered by 3D new metric survey technologies for 3D modelling reconstruction, this study presents a method or procedure of complete 3D data acquisition, using different sensors, and their possible fusion. Besides, this involved a discussion of the capability of UAV photogrammetry in order to collect data for the rooftop of the building with the low cost and combine the data with terrestrial measurement technique. Meanwhile, the aim of this study is to identify the minimum network configuration as to combine TLS and UAV photogrammetry data fusion. Hence, some procedure has been done in the methodology by registering TLS and UAV point clouds by employing multinetwork configuration. Furthermore, the data fusions’ results were evaluated on the registration error of UAV towards TLS coordinate system via the various number of network configuration samples. Based on the experimental results, the sample of network configuration for the three registration points results in a good condition due to the well-distributed registration points and less errors of both point clouds’ registration. As conclusion, a good quality of data fusion between TLS and UAV photogrammetry is determined by a good selection number of the registration points via several samples of network configuration.

Terrestrial laser scanners self-calibration study: Datum constraints analyses for network configurations

Similar to other electronic instruments, terrestrial laser scanner (TLS) can also inherent with various systematic errors coming from different sources. Self-calibration technique is a method available to investigate these errors for TLS which were adopted from photogrammetry technique. According to the photogrammetry principle, the selection of datum constraints can cause different types of parameter correlations. However, the network configuration applied by TLS and photogrammetry calibrations are quite different, thus, this study has investigated the significant of photogrammetry datum constraints principle in TLS self-calibration. To ensure that the assessment is thorough, 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. Based on graphical and statistical, the analyses of datum constraints selection indicated that the parameter correlations obtained are significantly similar. In addition, the analysis has demonstrated that network configuration is a very crucial factor to reduce the correlation between the calculated parameters.

Data quality assurance for hybrid and panoramic scanners via self-calibration

Quality assurance (QA) is a crucial process to ensure the maximize accuracy of the data delivered to client. Equipped with many moving parts whose relative positions can change over time depending on use, handling frequency and care, the QA is essential for TLS. Furthermore, with rapid and dense three-dimensional (3D) data collection ability, TLS has gain interest for many accurate 3D applications (e.g. industrial surveying, deformation measurement and reverse engineering). The QA for TLS measurement can be performed through calibration procedures, whether via component or system calibrations. Due to the non-affordable facilities and tools by most TLS users required by component calibration, this study focussed on the latter approach which only requires a room with appropriate targets. By employing optimal network configuration, system calibration was performed through self-calibration for hybrid (Leica ScanStation C10) and panoramic (Faro Photon 120) scanners. Four calibration parameters (e.g. constant range (a0), collimation axis (b0), trunnion axis (b1) and vertical circle index (c0) errors) were derived from 138 well-distributed targets in a laboratory with dimensions of 15.5m (length) × 9m (width) × 3m (height). For accuracy assessment purpose, fifteen test points are established at calibration field using photogrammetric technique. Those test points then were used to graphically and statistically evaluate the improvement in accuracy between TLS raw and calibrated data. As expected, the outcomes of statistical analyses have indicated an accuracy enhancement, for both scanners, respectively of 11% for Leica ScanStation C10 (1.7mm) and 50% for Faro Photon 120 (1.8mm) scanners.