ABSTRACT
Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry is a portable and cost-effective method for digitizing and mapping rock constructions, such as tunnels and slopes, into three-dimensional (3D) models. Scaling and orienting these 3D models are crucial for accurate assessments of stability, displacement, and risks in underground spaces. Photogrammetric 3D models can be scaled and oriented using known measurements, such as coded markers and reference points. Scaling methods include individual markers (1D), scale bars (2D) and scale cube (3D). In this study, a drift was photographed using a smartphone while three scaling methods, including individual markers, scale bars, and scale cubes were used. 3D models of the drift were reconstructed using SfM-MVS photogrammetry. The accuracy of the calculated distances obtained with these methods was compared to the known distances. The results show that using scale bars improves the accuracy of scaling. Additionally, this comparison demonstrates the effectiveness and user-friendliness of the scale bars for scaling 3D models and analyzing data.
