Laser-scanning of complex cave systems and animated cave visualisation
ISBN 978-85-88783-11-9
Authors
1Buchroithner, M.F.
1Institute for Cartography, TU Dresden Email: manfred.buchroithner@tu-dresden.de
Abstract
Since the advent of high-precision and comparatively light-weight terrestrial laser-scanners (TLSs) new, so far undreamt-of possibilities presented themselves to the caving community. Giving examples from Alpine and tropical caves, the idiosyncracies of cave laser-scanning and of adequate cartographic cave visualization a set forth. Initially, confining conditions stemming from the difficulties of accessibility (need to climb), darkness, temperature, air humidity and dirt of different kinds are dealt with. Making reference to one of the first laser-scanning campaigns in a difficult to climb cave, the Dachstein Southface Cave in the Austrian Alps, in 2007, the difficulties of working in a “cold” cave are exemplified. These conditions are still exceeded when working with a TLS in the biggest ice cave on earth, the Eisriesenwelt (Ice Giants World), also situated in the Austrian Alps. Here, in two subsequent surveying campaigns in 2011 and 2013 the dynamics of the ice filling have been investigated. Taking this example, also the difficulties of an adequate photorealistic image texturing are described. From the tropical regions of the world two extremely complex cave systems in the Malaysian part of Borneo are presented: Niah and Gomantong. Whereas in the first one only key parts, i. a. the world-famous Painted Cave, a cultural heritage of global rank, have been scanned and documented with the corresponding image textures, the Gomantong Cave System has been scanned completely. It represents the prime site for swiftlet nest harvesting in Borneo and is thus of multiple interest. Based on the point-cloud data of two National Geographic expeditions in 2012 and 2014 the so far most comprehensive virtual 3D cave model has been generated. Some examples of the extremely exposed scanning positions, sometimes hanging on drilled pitons in vertical or slightly overhanging rockfaces, in some cases more than 60 meters above ground, are set forth. Here, the advantages of a full tiltability, light weight and low energy consumption of a TLS, like the FARO Focus 3D TLS, are invaluable and almost a prerequisite. Finally the aspect of an optimized depiction of these complex cave systems is treated. Based on in-depth deliberations and tests carried out by the author the one and only way of generating a best-possible mental map of an intensely ramified cave at various levels turned out to be animated visualizations. Both, the views from outside the caves per se – be it from outside a mountain massif or from “within the mountain” but giving an overview – and fly-though simulations have to be presented in a synergetic way in order to enable individuals who have not the least idea of the respective cave system to generate a mental 3D map. Furthermore, an example of a high-quality classical planar cave map derived from laser-scanner data is given. It represents the so far most accurate cave map designed in the traditional UIS style.