## 3 Experiment and Analysis
### Experiment on Coastline Extraction at the Cliff
To reflect the relative positional relationship of the point clouds of the optimal coastline, centroid, and cliff, three-point cloud datasets were superimposed and are displayed in Figure 10a. The elevation of the optimal coastline points was closer to that of the water body, and their spatial height was closer to the water surface. Figure 10b shows an enlarged view of the red box in Figure 10a. As the coastline of the cliff is only a small segment, it must be fused with the point cloud of the coastline outside the cliff. According to the boundary point cloud of data extracted in the previous step, the coastline of the entire sea area could be obtained by replacing the point cloud of the cliff segment with the point cloud of the optimal coastline. To depict the difference between the point cloud of the merged coastline and that of the original boundary, these datasets were superimposed and are displayed in Figure 11a. The red segment and arched point cloud in the figure represent the point cloud dataset of the original cliff-segment boundary. Since the water body has a plane-pushing property, the original cliff segment boundary cannot clearly represent the actual coastline. However, for the point cloud behind the red segment, the blue segment calculated from the data is closer to the actual coastline and can reflect the shape of the coastline more accurately. Subsequently, a point cloud completion method [5] was used to complete the appropriate points according to the distance between the two points. When the distance between two points is less than 0.5 m, two points are interpolated: when the distance is greater than 0.5 m and less than 1 m, four points are interpolated. When the distance is greater than 1 m and less than 2 m, six points are interpolated; when the distance is greater than 2 m, eight points are interpolated, and the coordinates of the interpolated points are calculated from the coordinates of the original two points according to the corresponding proportion. The point cloud of the integrated coastline was completed according to this method, and the point cloud \(\text{P}^{\prime}_{\text{line}}\) was obtained, as shown in Figure 11b. Based on the average high-tide surface elevation \(\text{H}_{\text{MHWS}}\) determined by the hydrological observation data of Longkou City, Shandong Province, the point cloud of the coastline in a strict sense was extracted and recorded as \(\text{P}^{\prime}_{\text{line1}}\). Then, the points in \(\text{P}^{\prime}_{\text{line1}}\) were supplemented to obtain the point cloud \(\text{P}_{\text{shoroline}}\), as shown in Figure 12a. Points in \(\text{P}_{\text{shoroline}}\) were sorted from small to large according to their x-coordinates and connected to obtain the coastline trend, as shown in Figure 12b. Figure 7: (**a**) Rough extraction of point cloud in cliff segment. (**b**) Extraction of point cloud in cliff segment in combination with the x coordinate interval of points A and B.  
Figure 8: (**a**) The point cloud of centroid. (**b**) Superposition display of point cloud of centroid and point cloud of cliff. (**c**) The enlarged view of the red box in Figure (**b**). Figure 9: (**a**) Projection point cloud of side points \(\text{P}^{\prime}_{\text{side}}\); (**b**) Point cloud dataset of optimal coastline. A superimposed display of the point cloud of the fused coastline and the corresponding point cloud of the coastal zone is presented in Figure 13.  
To analyze the generated coastline in greater detail, Areas 1 and 2 in Figure 13 are enlarged and displayed in Figure 14a,b, respectively. Figure 11: (**a**) Superposition of point cloud of coastline after fusion and original boundary point cloud; (**b**) The completion of point cloud of coastline after fusion. Figure 10: (**a**) Superposition of point cloud of optimal coastline and centroid and point cloud at cliff; (**b**) The enlarged view of the red box in Figure (**a**). Figure 14: (**a**) The enlarged view of block 1; (**b**) The enlarged view of block 2.