Advantages and Limitations of Terrestrial Laser Scanner (TLS) and Photogrammetry Technology for Rock Slope Assessment in Malaysian Tropical Terrains

The application of Terrestrial Laser Scanner (TLS) and photogrammetry technology becoming common now for rock slope stability assessment. This paper discussed the advantages and limitations of TLS and photogrammetry methods in Malaysian tropical terrains based on several case studies. Excessive weathering in tropical terrains greatly affected the data capturing process. The limitations’ effects can be reduced through various combination of techniques and understanding the limitations, such as occlusion, orientation bias, resolution and truncation. Site limitations that are affecting the resolution and accuracy of the data captured and coverage including height and steepness of the slope; limited working area and time for data acquisition phase; hindrances overlay the slope face and external noise are also being discussed. The TLS position is important to reduce noise and interference, whereby correct positioning of TLS may reduce the orientation bias and allow the laser to reach slope face without occlusion. The manual scanline survey is still needed to calibrate data collected by TLS. Scanline survey provided actual visual identification of discontinuities planes in order to differentiate with mechanical breaks that can be mistakenly inferred during point cloud data processing phase. Classification and analysis of point cloud data can be speed up with available processed scanline data. Scanline survey also enable geologist to acquire trace joint data (low persistency, low relief and small plane surface area) which is not the case for TLS. Combination of photogrammetry, TLS and Unmanned Automated Vehicle Light Detection and Radar (UAV LiDAR) is proposed for complicated site in tropical terrains.