Constructing a True 3-D Model of a Karst Cave Using an UAV

Karst caves constitute an essential element of natural landforms. Construction of an accurate 3-D model of karst caves is crucial to guide geological exploration, underground space development, and safety in building construction and operation. Karst caves' subterranean location and various challenges such as weak lighting, attenuated satellite positioning signals, texture degradation, and unstructured surface scenes make true 3-D modeling of underground spaces challenging. Current methods of true 3-D modeling rely mostly on expensive and complex lidar scanning combined with ground mobile platforms or supplemented light source photography and multi-view stereo reconstruction. However, these methods are costly for karst cave reconstruction. Our proposed method for reconstructing the true 3-D model of the cave relies on the adaptability of a depth camera to low light environments. It is based on the data captured by an onboard depth camera of a drone for visual autonomous positioning and the surface reconstruction of unstructured scenes. We reconstructed the true 3-D model of Xuansu Cave located in Chibi City, Hubei Province, China. Experimental results demonstrate that the proposed method has the potential to reconstruct the true 3-D model of the underground karst cave surface efficiently and with stability. Furthermore, the use of light and small drones equipped with depth cameras presents a low-cost solution. These drones provide fast and reliable exploration of underground caves and offer true 3-D model reconstruction capabilities.