# Photogrammetry-Based 3D Textured Point Cloud Models Building and Rock Structure Estimation
###### Abstract  
Trace lines on the outcrop of a rock mass are usually the primary data source for the estimation of rock structure. It is important to obtain the data of trace lines precisely. Photogrammetry is well suited to finish this task. However, this is mainly conducted by commercial software, and not every researcher has easy access to the method of digital photogrammetry. This study aims to provide researchers with a low-cost method of building a photogrammetry-based textured 3D point cloud model (FMBPM) and display the applicability of the method to estimating the rock structure of rock masses. In the FMBPM, a digital single-lens reflex camera with a prime lens and a total station are the necessary hardware employed to capture images and measure the coordinates of feature points. A coordinate transformation means of converting model coordinates to physical coordinates was introduced. A program for calculating a joint orientation based on the coordinates of inflection points on the trace line of the joint was developed. A section of a rock slope was selected as a case to show the procedures and the practicability of the FMBPM. The textured 3D point cloud model of the rock slope was successfully built, and the rock structure of the rock slope was analyzed using the joint disk model generated based on the trace lines extracted from the point cloud model. The results show that: (1) the precision of the point coordinates of the textured 3D point cloud model could achieve 3.96 mm, taking the data of the total station as the reference; (2) the rock structure of the slope is good, according to the value of the rock quality designation; (3) the new method is applicable in engineering practices. photogrammetry; rock structure; coordinates transformation; joint disk model 20231349720233/10.390/app13084972023/10.390/app13084972023/10. inaccessible. Yet, the detailed rock structure information of the inaccessible areas is also urgently needed to ensure the stability of the engineering. Consequently, remote sensing techniques are being used increasingly, which permits a safe, fast, comprehensive, and accurate acquisition of information on inaccessible rock exposures and increases engineer safety. Digital photogrammetry and laser scanning are two main methods of remote sensing techniques related to rock engineering, both of which can generate high-precision 3D point clouds of research objects [7; 8; 9; 10]. Laser scanning methods generate a point cloud model using time-of-flight technology [11]. In comparison, digital photogrammetry methods calculate the spatial coordinates of a point based on its planar geometric position in different photographs. Many studies related to rock structure extracting and geological hazard analysis have been conducted based on the two methods. [PERSON] et al. [6] presented a method for evaluating the development of the joints on rock tunnel faces based on a 3D point cloud model obtained by photogrammetry. [PERSON] et al. [12] estimated the dynamics and sizes of landslides by comparing digital terrain models, which are generated photogrammetrically from stereo pairs of images. [PERSON] et al. [13] demonstrated the effectiveness of Unmanned Aerial Vehicle photogrammetry in the remote sensing and assessment of landslide behavior through a case study of a landslide that occurred in Guizhou, China. [PERSON] et al. [14] provided a tool for the semi-automatic damage assessment of roads in landslide-affected areas to support the risk analysis and planning of mitigation measures based on photogrammetry. [PERSON] et al. [15] determined the block size and shape distributions according to a textured digital surface model of an investigated outcrop. [PERSON] et al. [16] detected joints on the surface of a rock slope based on digital photogrammetry and a remotely piloted aircraft system. [PERSON] et al. [5] searched the dangerous parts of a rock slope using block theory based on photogrammetry. [PERSON] et al.