Can 3d scanning become an actual cartography technique?

Photogrammetry can create detailed maps for underground facilities with irregular shapes. However, for straight and long corridors, traditional mapping techniques may be more suitable. 3D scanning can improve safety in tourist diving by providing divers with a three-dimensional model of the dive site. While the effectiveness of reducing stress is difficult to determine, personal experiences suggest that familiarization with the site can be helpful.

It might seem obvious that one of the main reasons for scanning caves and mines is the popularisation of these sites. What about other possible benefits of underwater overhead cartography? How about cartography for instance?. Photogrammetry is one of many techniques that we can use to create a detailed map of an underground facility, be it a cave or a mine. I will make a reservation here that I personally see more sense in scanning caves, the highly irregular shapes of which justify the use of a 3D scan.

Let us remember that photogrammetry is only a tool serving a specific purpose. When starting a demanding project of documenting underwater corridors, let's always ask ourselves: 'Why am I doing this' and 'what will I find there?' It may turn out that our goal is to make a map, and our facility is a mine consisting of straight and long corridors of considerable length, e.g. over 10 km. - let's then abandon the idea of scanning and use traditional mapping techniques - i.e. a laser disto, a compass and an underwater notebook.

An astute reader might say, after all, we are talking about documentation of the mine using the photogrammetry method, and the author himself says that it is a bad idea?' I hasten to answer that in some respects - yes, tragic. If, as indicated at the beginning, I intended to create only a map of corridors, I would follow my own advice and limit myself to writing down basic parameters such as azimuth, depth and length of each section. However, this activity would have limited sense because - in the case of the Maria Concordia mine described here - a map of the most extensive corridor at a depth of 8 m below the water level already exists and is easily accessible. The deeper levels are much less complicated. So let's move on to the second possible purpose of performing the scan - improving safety in tourist diving. One of the factors that significantly affects diving safety is the diver's psychological comfort - in reasonable doses, of course, because in excess it can lead to unnecessary bravado. Diving in a new, unknown place is a stressful factor - even if we don't want to admit it to ourselves. In such conditions, any failure under water, whether it is loss of visibility or a hardware problem that must be solved immediately, is another brick in the stress pyramid, where the current foundation is being in an unknown space. Can getting acquainted with a three-dimensional model of the place where we will dive reduce this stress? And if so, to what extent? It is difficult to answer this question definitively, primarily because it is impossible to conduct a reliable study. Performing scans of significant parts of flooded caves and mines is a relatively new activity; you can count on one hand how many such objects in Europe have been documented in this way.

Fontanazzi Cave - an example of an irregularly shaped tunnel. Author of the model - Bartek Pitala. Poster made in collaboration with Submerged Foundation

However, I can share my personal experience. Several people with outstanding achievements in cave exploration cooperate with the Submerged foundation I run, including our compatriot Bartek Pitala. One day I read Bartek's scan of a rather complicated entrance to the Italian Fontanazzi cave. This cave is known for a series of restrictions (narrow passages) protecting the entrances to further parts. After completing several virtual 'dives', I had no problems with navigation, so I can say that this type of familiarization with the place we intend to visit makes perfect sense and reduces at least one stress factor. Following this line of thought - some time ago I talked to my friend Mikko Paasi from Finland, who was involved in the rescue operation in the Thai cave Tham Luang. He recalled a situation when, while evacuating boys trapped there, he and other participants had to squeeze through a rather narrow opening (well under a meter in diameter) (with zero visibility!). They had no choice because that was the way the handrail led them, i.e. the ropes showed the way to the exit. Only after the action, when the water had subsided, it turned out that the hole had the shape of a keyhole, it was enough to move the life line a by several dozen centimeters to the place where the hole widened to make it possible to swim through relatively comfortably - but no one knew about it at that time and in the absence of visibility any 'experiments' may end tragically.