## 1 Introduction  
With the development of the social economy and the increase of national infrastructure investment, the scale and complexity of rock engineering have been increasing. The mechanical characteristics of the rock masses involved are becoming more and more complex. Rock masses differ from rocks in that they contain many discontinuous structural surfaces. Fractures are common discontinuities in rock masses [1, 2] that intersect each other to form complex fracture networks. Fracture networks are an important reason for the extremely complex deformation characteristics of rock masses. The nonlinear, size effect, and anisotropic behavior of fractured rock masses are affected by their complex fracture networks [3, 4]. The instability of rock masses is usually caused by the deformation, expansion, and penetration of the fractures in the fracture networks [5, 6]. Additionally, the strength and deformation parameters are controlled by the complex fracture networks [7]. The complex fracture networks are usually determined by fracture geometry parameters, such as inclination, dip angle, and trace length of the fractures. Therefore, it is of great importance to study the influence of fracture geometry parameters on the mechanical properties of a rock mass. Identifying and extracting fracture geometry information is essential for analyzing the mechanical and deformation properties of the fractured rock masses. There are two main ways to acquire a fracture's geometric information in an outcrop area, includingcontact and non-contact measurements. The efficiency of contact measurement is lower, and the measurement accuracy cannot be guaranteed [8; 9]. In recent years, non-contact measurement techniques (such as total station and photogrammetry) have been widely used to analyze fracture geometric information in a rock mass. It can effectively capture data from physically inaccessible areas [10]. Laser-scanning techniques are an effective non-contact measurement method. By analyzing the outcrop characteristics of visible fractures on the rock mass surface, point cloud data processing can be used to identify discontinuities and extract information from them [11]. A method to detect and estimate the orientation of plane structures was proposed based on the principal component analysis (PCA) techniques by [PERSON] et al. [12]. When applied to practical situations, it showed high precision in both the detection and location of fracture planes. A method for generating a high-resolution digital outcrop model (DOM) of the rock exposure based on UAV photogrammetry and the structural self-motion (SFM) technique was introduced and applied to slopes in Greece and China [13]. The results showed that UAV-SFM photogrammetry had higher efficiency and operability, especially in difficult measurement environments. Stereophotogrammetry is a method of extracting the regions of interesting information by constructing stereo images from two or more photographs. ShapeMetriX\({}^{\text{3D}}\) is widely used for discerning the structural surface information statistics of rock slopes and tunnels [14; 15; 16]. The close-up photographs turned out useful to obtain detailed images and accurate results. The distribution of fracture geometry parameters has certain statistical and probability distribution characteristics. Statistical methods are often used to quantitatively describe and analyze fracture geometry parameters. The fracture distribution function is obtained based on a fracture's geometry parameters and statistical methods [17; 18]. The discrete fracture network (DFN) model provides an approach to characterize complex fractures based on the fracture distribution function [19]. The sizes, directions, spacings, and spatial locations of fractures are included in the DFN model. The DFN model is also an effective method to study the influence of fracture geometry parameters on the mechanical properties of complex fractured rock mass [20; 21]. The model consists of the fractures embedded in the rock.