Drain the Oceans: Thai Cave Rescue – A Nat Geo documentary

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As a result of our numerous cave scanning assignments, Commendium were contacted by MSP TV to assist them with an episode of the ‘Drain the Oceans’, a series on behalf of Nat Geo TV. Having worked for The National Geographic on several occasions, it was great to be back.  

Our brief was to 3D survey a 6km stretch of the Tham Luang cave passages in Thailand, using LiDAR terrestrial scanners. The data from the scans would be processed to make a photorealistic CGI 3D model of the cave journey. The 3D model itself illustrates part of the Thailand Cave Rescue story deep in the Chiang Rai province.

Prior to setting off we were looking at a hand-drawn cave survey of the Tham Luang cave system, completed by its first explorers. Looking at the illustration it was immediately clear that this was going to be one of our more demanding projects, 6km of often narrow, invariably humid and muddy cave passages. We estimated it would take three weeks, to scan the caves and a complete surface survey of the area.

The Challenge

The cave system proved to be every bit as challenging as we had imagined. In the dry sections, the cave was very easy to navigate for experienced cavers, however, then came the slippery section with lots of clambering over large boulders. With each of us carrying about 20kg, the humidity was draining for the crew.

We opted to scan from the furthest point inside the cave and work our way through to the entrance. This was mainly for psychological reasons, for every subsequent surveying day required less travel to the start and so became easier, though most days underground were more than ten hours. One job was to record the cave texture through photography. It is amusing to put one of the world’s leading caving photographers to such repetitive work, but the discipline to ensure that everything is recorded meticulously is probably the single hardest aspect of 3D data capture. We tried to work to three days and then rest on the fourth, however, in practise, our rest days and evenings were spent processing the vast amounts of scanned data. Our drone operator meanwhile was travelling above ground capturing the surface terrain data.

Capturing Data

By the end of the project we had gathered almost a terabyte of data, which takes some managing, but again, with our procedural disciplines in place we ensured we captured all the data required. We had loosely stitched 400 LiDAR scans together in the field, to check for any parts of the cave we may have missed, however, all was looking good.

With all the data gathered, we found ourselves quite sad to leave Thailand at the end, having made many solid friends, it was a very emotional journey.

Once back in the UK the real work began. The photos were processed to colour-match and check level brightness. The scans were re-stitched and cleaned up to eliminate noise and unnecessary items, such as people. The scans were also adjusted with GPS co-ordinates, to ensure the cave would be orientated correctly when we merged both the surface scans and underground models. Meanwhile, we processed the drone imagery into a surface model. There were a few problems, as the conditions had been quite cloudy, but skilful low flying, cloud-dodging, and waiting for conditions to improve, meant that a superb model accurate to within 10cm was produced. The next phase was working with the VFX (visual effects) team. Over several weeks we created several models to create CGI imagery for the film. We built an animated diver, constructed sections of the cave in meticulous detail, tested various animations and effects. The final result is superb. We look forward to the broadcast of Drain the Oceans: Thai Cave Rescue in the UK on the 6th of January, 2020 on the Nat Geo channel.