Hidden Earth 2019

Mobile Handheld 3DLaser Scanning - Cave Surveying of the Future

45 minute Lecture|Madphil

Abstract

Until the last decade, cave surveying was a pretty simple affair; the measurement of a baseline using a tape, compass and inclinometers, guestimation or actual measurement of passage dimensions (LRUD), followed by the sketcher drawing an "Artists impression" of the cave passage either to or not to scale. This data would then be put into both cave surveying and drawing packages to produce a final survey. Dependant on the skill of the sketcher, these "Artists impressions" could be at best similar or at worse bare no resemblance to each other at all!

The advent of laser distance measurement and increasing computer and phone technology has more recently transformed cave surveying. More commonly a DistoX (a laser distance measurement device with a electronic compass and inclinometer built-in, connected via bluetooth to a PDA, tablet or a mobile phone has lead to a new breed of paperless survey packages allowing more accurate measurement of legs and drawing splays (via the DistoX), which is automatically transmitted to the PDA or phone, where the cave surveying software allows the data to be displayed to a user variable true scale, on which the cave survey can be drawn with lines, symbols and area representing all the cave surveying symbols. As a result the cave survey produced by this method is generally of far superior quality. Despite this however, the survey generated is still the sketchers "Artist Impression" of the cave passage.

In parallel with this, the increase in computer power has led to the appearance of 3D laser scanners. Tripod based machines, that can do a "360" degree scan of the area, with ever increasing number of points, accuracy and speed. The 3D point cloud generated gives an exact representation of the cave passage with all features located accurately. While cumbersome and slow to use in a cave, the data sets in larger passages/chambers have proven very successful, but for more complex caves prove very time consuming due to the complexity of geo-referencing each scan.

In 2012, a new generation of mobile handheld 3D scanners appeared and warranted a step change in both cave surveying and 3D scanning. These handheld devices can scan on the fly while walking through the cave, (with no requirement to fixed the scanner on a tripod at a known location). The software cleverly pieces the random scan data back together to produce a 3D image of the passage surveyed. It is now even possible to see the data being collected real time while scanning.

This presentation discusses the use of these mobile handheld 3D scanners, the research conducted in a number of case study caves, and highlights the benefits, pitfalls, the results produced and where the technology is currently going.