Full size cave 3D modelling using close range photogrammetry and comparison with laser scanning

Although underground topography methods have significantly evolved in the past two decades, it is still challenging and often costly to create comprehensive 3D models of caves or artificial cavities. Modern methods used by speleologists, involving the generation of a topographic ‘skeleton’ through laser pointer measurements, enable surveying extensive developments but suffer from a lack of resolution. Conversely, the use of Lidar technologies, while capable of obtaining sub-millimeter scans, implies the use of expensive equipment and precision electronics often unsuitable for this harsh underground environment. In this study, we propose to test the use of low-cost cameras (action-cam type) for the complete 3D modeling of a cave through photogrammetry aiming to compare the results with a Lidar survey based on a series of topographic markers precisely measured with a total station. Our findings indicate that photogrammetry is an approach significantly faster and more adaptable in the field, leading to a substantial reduction in artifacts and shadows compared to static Lidar usage. Although post-processing involving image correlation is more computationally intensive for photogrammetry, we explore various strategies to reduce the calculation times. Ultimately, we demonstrate that the residual positioning errors on the topographic markers are of similar centimetric magnitude to those of Lidar. Recent advancements in computing capabilities now make it feasible to consider the use of photogrammetry for extended underground developments, presenting a promising alternative to the more conventionally employed Lidar in such contexts.