# A UAV Coverage Path Planning Method Based on a Diameter-Height Model for Mountainous Terrain
## 4 Experiment and Discussion  
The proposed UAV coverage path planning method based on the DH model for mountainous terrain has been implemented in MATLAB language, and all the results are rendered via the MATLAB plot function tool (2024a). In the simulation experiment, a quadrilateral is taken as an example to represent a simplified mountainous terrain containing three mountains, as shown in Figure 2. In virtue of the proposed DH model, the simplified 3D map of the mountainous terrain can be constructed with a side length of 2000 pixels. The safe threshold distance \(\delta\) is set to 50 pixels, and the coverage path width \(L\) is set to 100 pixels. The statistical parameters of the DH models in the 3D map are summarized in Table 1, and the default unit for all parameters in the table is pixels. The constructed 3D map is loaded into the proposed CPP method based on the DH model, and the generated coverage path can be illustrated in Figure 9. Three DH models are drawn in light green, light red, and light blue, respectively. The generated global coverage path consists of blue lines and red lines. As mentioned above, the blue lines indicate the equal-interval spiral ascent paths and the equal-interval circle paths. The red lines are the auxiliary connection paths with trajectory minimization and obstacle avoidance. From the experimental results, it can be seen that the simplified mountainous terrain can be well covered, providing good conformal coverage effects, and the effectiveness and feasibility of the proposed UAV coverage path planning method based on the DH model can be verified. In order to demonstrate the energy-saving advantage of the proposed CPP method based on the DH model, a comparative experiment was conducted, and a classic zigzag coverage path planning algorithm [32, 33] was implemented using MATLAB language and directly applied to the same constructed 3D map of simplified mountainous terrain. Since the zigzag coverage method excels at covering the flat areas but has poor coverage effects for regions with the high mountains, in practical applications, a feasible solution to apply the zigzag coverage method on the mountain coverage is to raise the path planning plane to a certain height, ensuring that no obstacles or mountains occur in this plane. \begin{table}
\begin{tabular}{c c c c c c} \hline
**DH Model** & **d1\({}^{\textbf{1}}\)** & **d2\({}^{\textbf{1}}\)** & **h1\({}^{\textbf{1}}\)** & **h2\({}^{\textbf{1}}\)** & **Position \({}^{\textbf{1}}\) (x, y, z)** \\ \hline DH\({}_{1}\) & 400 & 200 & 387 & 173 & (500,250,0) \\ DH\({}_{2}\) & 800 & 500 & 581 & 433 & (1500,1000,0) \\ DH\({}_{3}\) & 600 & 400 & 484 & 433 & (600,1000,0) \\ \hline \end{tabular} \({}^{\textbf{1}}\) all parameter values are measured in pixels.  
\end{table} 
Table 1: The statistical parameters of DH models in 3D map of simulation experiment. However, it cannot be denied that this compromise will inevitably lead to poor coverage effect, as the coverage path lacks the advantage of terrain adaptation. Taking the detectors mounted on UAVs, such as cameras, as an example, when the coverage path is planned at the high position, in order to ensure that the clarity of the captured image is not reduced, it is necessary to replace the short-focus lens of the camera with a long-focus lens. However, compared to the short-focus lenses, the long-focus lenses have a narrower viewing angle; in other words, the width of the trajectory for covering mountain terrain needs to be reduced accordingly. Inevitably, the coverage path generated by the zigzag method has a denser path feature and longer path length. Without loss of generality, the trajectory width is set as 25 pixels in the coverage path planning method based on zigzag, and the simulation results are shown in Figure 10. Obviously, the generated zigzag coverage path is denser than the one generated by the proposed method.