## 1 Introduction  
The positional accuracy of UAV geospatial products is affected by numerous factors, including the nature of the survey area and its morphological characteristics [1]. The other main factors that affect the positional accuracy of UAV products are the model of the UAVs, the type and accuracy of the navigation and orientation instruments on board the UAVs, the camera specification, the ground sensing distance (GSD) [2], the degree of overlap, the UAV flight altitude, and the number and configuration of ground control points (GCPs) [3]. Several previous studies have analyzed and investigated the effects of these factors on the positional accuracy of UAV products [4]. In general, the positional accuracy of UAV products has been tested and analyzed in some studies and research as follows [5]:  
In 2015, [PERSON] and [PERSON] used GCPs and Pix4D software to photogrammetrically map a gravelly river channel and achieved a horizontal accuracy of 0.048 m (RMSEH) and vertical accuracy of 0.035 m (RMSEZ), which were compatible with the accuracy standards developed by the American Society for Photogrammetry and Remote Sensing (ASPRS) for digital geospatial data at the 0.1-m RMSE level [6]. Next, [PERSON] et al. (2016) compared the spatial resolution of three cases of UAV imagery acquired during two missions to a gravel pit. The first case was a surveillance-level GNSS/RTK receiver (direct georeferencing), the second was a lower-level GPS receiver (direct georeferencing), and the third was a lower-level GPS receiver with GCPs (indirect georeferencing). The horizontal and vertical accuracies were RMSEH = 0.032 m and RMSEZ = 0.120 m in the first case, RMSEH = 0.843 m and RMSEZ = 2.144 m in the second case, and RMSEH = 0.034 m and RMSEZ = 0.063 m in the third case, respectively [7]. Later, [PERSON] and [PERSON] (2018) evaluated and analyzed the positional accuracy of UAV mapping with onboard RTK without GCPs compared with UAV mapping without RTK with different numbers and configurations of GCPs. In the case of the non-RTK method with GCPs, the horizontal and vertical accuracies were 4.8 and 8.2 cm with 5 GCPs, 5.4 and 10.3 cm with 4 GCPs, and 6.2 and 12.0 cm with 3 GCPs, respectively, depending on the number of GCPs. The horizontal and vertical accuracies of the non-RTK method without GCPs deteriorated to about 112.9 and 204.6 cm, respectively. The horizontal and vertical accuracies of the RTK-onboard-UAV method without GCPs were 13.1 and 15.7 cm, respectively [8]. In addition, [PERSON] et al. (2020) investigated the influence of the number of GCPs on the vertical positional accuracy of UAV products. This study was conducted on sandy beaches in China. The authors concluded that the number 11 was the optimal number of GCPs in this study area and had a vertical RMSE of about 15 cm [9]. Further, [PERSON] et al. (2021) investigated georeferencing of UAV imagery aboard GNSS RTK (without GCPs). The researchers evaluated and analyzed the reasons for the high-altitude error, which is a challenge for this technique. They proposed strategies to reduce these types of errors. Several missions were conducted in two study areas with different flight altitudes and image-capturing axes [10]. This study showed that a combination of two flights at the same altitude but with vertical and oblique image acquisition axes could reduce the systematic vertical error to less than 3 cm. In addition, this study demonstrated for the first time the linear relationship between the systematic vertical error and the variation of the focal length. Finally, this study proved that georeferencing without GCPs is a suitable alternative to using GCPs. All these studies have produced important results and paved the way for further studies. However, few studies have addressed the effects of camera orientation on positional accuracy. Similarly, there have been no studies that have addressed the effects of the direction of the flight lines and their position within the study area on the positional accuracy values.