## 1 Introduction  
The collapse and slide of a mountain slope is a common natural disaster that threatens the safety of buildings and people's lives and property. Landslides cause the deaths of thousands of people every year, and the direct economic loss exceeds hundreds of millions of USD. Therefore, deformation monitoring and stability analysis of the slope are very important. Currently, the commonly used slope displacement monitoring methods include laser ranging, GPS observation, remote sensing, and close-range photogrammetry [1; 2; 3; 4]. In the traditional close-range photogrammetry method, the slope is monitored by setting landmarks and collecting data at different positions using a camera. The total station is used to measure the control points, and software is used to carry out internal processing such as aerial triangulation. The results before and after the deformation are compared, yielding the deformation within the corresponding time section. The measurement accuracy of slope displacement monitoring by close-range photography may not be as good as some traditional measurement methods [5]; however, it fully meets normal monitoring requirements. The rapid development of close-range photogrammetry has enabled different applications in aerospace, archaeology, architecture, bridges, and other fields [6; 7; 8; 9]. The development of GPS technology and its combination with close-range photogrammetry exploits GPS measurement advantages and solves some positioning problems in close-range photogrammetry [10; 11]. Due to the inconvenience of control-point measurement, some researchers applied the photogrammetry method to detect the size of the target object without a control point, considering the physical parameters of the camera [12]. Several researchers used close-range photogrammetry technology to generate a digital elevation model (DEM) and obtain the movement of the slope area using DEM subtraction of multi-period data [13; 14]. [PERSON] et al. [15] and other researchers employed close-range photogrammetry technology and the block analysis method to analyze the rock mass failure of a slope DEM. Furthermore, close-range photogrammetry technology can be used to produce a digital terrain model (DTM) and a digital orthophoto model (DOM), and obtain 3D point cloud data. [PERSON] et al. [16] used these methods to monitor slopes. [PERSON] et al. [17] combined close-range photogrammetry with surface modeling to predict landslide trends. Without any control points, [PERSON] et al. [18] used the Moore-Penrose generalized inverse matrix to analyze the equation derived from the geometric relationship between the camera, the measuring point, and the shooting image, and obtained the distance between the measuring points installed on the target slope. The purpose of dynamic monitoring of the slope was achieved via the change in the distance. Close-range photogrammetry is widely used in slope displacement monitoring. However, the close-range photogrammetry method also has shortcomings: The data processing is cumbersome, the degree of specialization is high, it is vulnerable to terrain restrictions, and the relevant hardware equipment is expensive. Using the measurement principle of white light speckle, [PERSON] [19] used a non-metric digital camera to verify its performance in building deformation monitoring. However, the effect of digital camera calibration on the results was not considered. [PERSON] et al. [20] programmed to call the camera's Software Development Kit (SDK) to achieve automatic control of the photography and used a GPS wireless network to achieve data exchange and remote control of the camera so as to enable real-time monitoring of slope displacement by the remote-control camera. Nevertheless, the real-time displacement of the digital camera was not considered. This method can only monitor slope displacement when the digital camera position is fixed.