A new method for constructing roads map in forest area using UAV images

High definition map is a map used for automatic driving. Its absolute precision is sub meter level, that is, the error between the position of an element on the map and the position of the element in the real world is less than 100 cm. In addition, compared with ordinary maps, high definition maps contain more geographic information, such as road width, slope, curvature, etc. At present, high definition roads map construction is largely for the main traffic road. However, there are few studies on the construction of high definition forest roads map for forestry production and management. Thus, it is imperative and helpful to explore an efficient and low-cost method for constructing high definition forest roads map that can provide accurate basic map services for forestry management activities. In this study, firstly, the DJI Phantom 4 RTK UAV was used for aerial photography to obtain the forest oblique images. Then, combined with close range photogrammetry, the high-resolution images under the forest are acquired and generated into dense point cloud images. Next, the two images are fused using iterative closest point (ICP) algorithm combined with manual registration; Finally, the fine-grained 3D scene model is generated by using the Context Capture 3D modeling software, based on which a high definition forest roads map was constructed using human-computer interaction model. Taking Menggongshan Forest Farm as an example, the construction of the fine 3D scene model was carried out to solve the problem of loopholes and ambiguities of the road model under forest, based on which the high definition forest roads map was constructed. To evaluate the accuracy of the forest roads map, the accuracy check was conducted. The results showed that the point position on the forest roads map, compared to the actual point, had a medium, minimum and maximum error of 0.076 m, 0.020 m and 0.170 m in plane, respectively, a medium, minimum and maximum error of 0.122 m, 0.005 m and 0.214 m in elevation, respectively. The accuracy of the high definition forest roads map meets the need of forestry production and management activities. It is feasible to adopt the method of UAV oblique photogrammetry combined with close-range photogrammetry, fine 3D scene model construction and human-computer interactive for constructing high definition forest road map. And this method can provide a low-cost and high-efficiency way for constructing high definition forest roads map, and also can better provide basic map data for forest management activities.