Henno Morkel, LiDAR systems engineer and product specialist for ZEB1 in our South African office, gives us an in-depth account of one very unusual job that he and the mobile laser scanner were asked to complete recently…
3D Laser Mapping’s South-African office were privileged to do some 3D laser scanning with our hand-held mobile laser scanner ZEB1 recently, at Rising Star Cave. Situated in the Cradle of Humankind near Johannesburg South-Africa, this is the cave where the latest incredible archaeological find – dubbed Homo naledi (naledi coming from dinaledi meaning “the rising star” in the native Sesotho-language) has been discovered.
This archaeological find, consisting of around 1550 bone fossils representing 15 different individuals is considered to be the closest possible ancestor to our genus, Homo sapiens. The actual chamber which housed all of the newly discovered specimens was first discovered by a pair of recreational cavers Steven Tucker and Rick Hunter about two years ago. They then referred the find to highly acclaimed paleoanthropologist Lee Berger from the University of Witwatersrand in Johannesburg.
Lee Berger went on to recruit various anthropologists and archaeologist to excavate and examine the fossil chamber. The final chamber could only be accessed by a very long (almost 12m) narrow chute, which only ‘slimmer’ explorers could slide through. One of the researchers selected was anthropologist Marina Elliot from the Simon Fraser University in British Columbia.
Fig.1 – The ZEB1 mobile hand-held laser scanner
Marina Elliot had a great desire to document the Rising Star Cave with modern technology, especially that of 3D laser scanning, so she contacted 3D Laser Mapping to enquire about our mobile hand-held laser scanning solution, the ZEB1, manufactured by GeoSLAM – a UK based company situated in Nottingham.
Some 3D laser scanning of the Rising Star Caves has previously been conducted, but with a static terrestrial laser scanner. This method was not fit for the purpose of scanning in small spaces and tight crevasses, and also required a lot of different individual scanner setups. The ZEB1 laser scanner however is a portable device which easily fits inside a small backpack. The mobility of this advanced laser scanning technology allows the operator to walk and scan simultaneously, covering greater distances much faster.
The Rising Star Cave consists of a labyrinth of cave chambers and long narrow diagonal vacuums – this cave is definitely not for the claustrophobic. The purpose of this site visit was to show the ZEB1’s capability for scanning the cave site, and to determine if the ZEB1, and the data output given could be a good tool for them to assist in the 3D documentation of the cave.
I met up with Marina Elliot and her exploration team at the Sterkfontein Caves visitors parking area at 07:00 am the 2nd of July 2015, from there we drove to the Rising Star cave site. Marina and Wayne gave me a briefing about how the caves work and safety points, providing me with the necessary safety equipment like a hard hat with a cave light and an overall.
Fig.2 – Showcasing the ZEB1 mobile laser scanner and explaining the main principles of operation.
I then explained to the team how the ZEB1 scanning device works and we commenced scanning of the cave site, working our way inside into all its different chambers. In total we did eleven individual scans as we moved along downwards into the tunnel, each of them creating a closed loop as necessary for the ZEB1 workflow.
In total it took us 3-4 hours to scan 80% of the Rising Star Cave The total length of the cave measured from the scanned data was approximately +- 1.2 km, and we were descended vertically about 30m underground.
One of the main advantages for using the ZEB1 laser scanner to scan and document underground environments and caves, is that the data capture is mobile. You can walk or crawl around in the cave and ‘paint’ the areas with laser as you move along. This feature makes the ZEB1 laser scanner unique in that it uses technology borrowed from the field of robotics called – SLAM. (Simultaneous Localization And Mapping). This enables cave scanners/documentors/archaeologists or anthropologists to rapidly 3D scan a cave within 0 –3cm accuracy. This means that the deviation of error or difference between the scan data to the real world environment differs by +- 0 – 3cm.
The fact that the ZEB1 laser scanner is a mobile scanner also greatly improves its data capturing capability with regards to its reach and line of sight. The scanner has an indoor range of about 30 m, which means that the infrared laser beams spread and penetrate smaller gaps and crevasses which you can’t see with the naked eye.
Fig.3 – Top bird’s eye view of the point cloud data scanned; the points are coloured by elevation height, meaning red is the highest elevation and blue is the lowest elevation.
Fig. 4 – Right side view of the point cloud data from the Rising Star cave; the points are coloured by elevation height, meaning red is the highest elevation and blue is the lowest elevation.
Fig. 5 – An oblique view of final big chamber where Dragon’s back is situated, and this image also shows the superman crawl that one must go through from one chamber to the next.
Fig. 6 – A top view, cut in half horizontally, of one of the first chambers in the cave system
By analysing and looking at the laser point cloud results, it give the viewer or researcher an autoscopic view of the cave system, which can provide invaluable additional geometrical information about the cave, and maybe even show new entrances or different pathways within the cave that were previously unknown.
With the point cloud processing software available, one can dissect the scan data horizontally or vertically into different levels or layers, to do further analysis and inspection of a specific area within the caves.
After we ascended out of the cave, I processed the scan data and then registered each of the individual scans to each other to give the overall total picture of the cave system up to the dragon’s back which we did on the day.
Fig. 5 – Showcasing and explaining the ZEB1 scanner to a cave explorer.
Fig. 6 – Approaching through the Superman Crawl – a small tunnel, about 4m in length, in which cavers should extend their one arm in front of them, and hold the other arm on their side towards the back – i.e. Superman pose.
The ZEB1, has proven itself across the globe for being a truly fast, nimble and versatile laser scanner for scanning in tight areas. Some examples of cave sites which have been successfully mapped with the ZEB1 scanning system can be read about at these links:
Aboriginal Caves, The National Show caves of Wales ,Wookey Hole Cave , Cliefden Caves
Most recently the ZEB1 made history when it was used to map Brei Holm, a dangerous coastal cave in Papa Stour, one of the Shetland Islands in Scotland.
Read more about the ZEB1 for underground mining on our product page.