MODELING CARTER CAVES WITH STRUCTURE-FROM-MOTION PHOTOGRAMMETRY: A 3-DIMENSIONAL CAVE SURVEY

Researchers and explorers alike have experienced the limitations of cave mapping due to the fact that one cannot see much of the whole cave system from any single vantage point, making accurate surveying difficult and tedious, and because the variety of passage shapes and cave features are difficult to adequately portray using traditional survey techniques. This project aims to remove some of these limitations using the photogrammetric technique Structure-from-Motion (SfM) which uses sets of overlapping photos taken at multiple vantage points to create an accurate 3-dimensional model of the cave. High resolution imagery is then draped onto the model so as to give the viewer a virtual cave tour. The accuracy of this photogrammetric method as a viable stand-alone technique for cave mapping was tested at X-Cave at Carter Caves State Resort Park in Kentucky. Survey markers were placed throughout the cave system, and the distances between markers measured in the field using a disto-laser distance measuring tool. The SfM program Agisoft Metashape was used to process over 6,400 photos, and a 3-dimensional model of the cave was constructed which included the markers in the imagery. Marker distances within the model were then compared with surveyed marker distances to assess the accuracy of the model. The use of photogrammetry can reduce limitations to traditional cave mapping and provide not only an accurate map, but a more realistic and detailed cave map.