LIDAR SLAM & drones map WWII legacy

Argus Vision rediscovers the battlefields 

The Second World War has been a central theme in thousands of stories. Still, many of its secrets remain undisclosed. American TV channel Smithsonian Channel recently hired a British production house to produce a new documentary on this dark period. They wanted to reconstruct the story of the battlefields, using new technology. We looked after the Belgian narrative and mapped a site in Sankt Vith using SLAM based LIDAR and drones.In the end, our work provided a title role in the television series. 

The Belgian Ardennes during WWII 

In December 1944 and January 1945, the Belgian Ardennes were the backdrop of a battle that would indirectly affect the end of WWII. Adolf Hitler realised he had just one single opportunity left to turn the tide: a large attack by the German Wehrmacht at the Western front. He deployed 250,000 soldiers and 1,000 tanks, but the Allies did win this Battle of the Bulge. 

Sadly, this battle meant a blood bath in which tens of thousands lost their lives, even more were wounded. Till today, it is not clear what exactly went on, and especially the Sankt Vith site is shrouded in mystery. 

Photogrammetry not an option 

Today, no one really knows what WWII remnants are still around. That is the reason the production house wanted to reconstruct the most important battlefields, including a focus on the Sankt Vith site in Belgium. The intention was to intricately reconstruct what actually went on during the Battle of the Bulge.

“In most instances, photogrammetry is the solution of choice to visualise such sites. However, the Sankt Vith site consists of dense forests, making it impossible to use photogrammetry. In the end, the solution was brought forward by Dr Birger Stichelbaut of the School of Archaeology at the University of Ghent (BE). He contributed to the research regarding this battlefield and suggested laser scanning, since he had used this technique successfully in other cases”, explains Jonas Van de Winkel, Argus Vision’s co-owner. 

3D model required high resolution 

At first, the research team went to work with the height models made freely available by the government. “These images have been made with laser scanners attached to planes”, details Dr Birger Stichelbaut. 

“The laser scan images have been rendered with very specific software for archaeological research, providing a large amount of interesting information. They have for instance been instrumental in mapping several World War I sites in Western-Flanders. But the resolution of these images is rather limited: 1 pixel per sqm, which proved insufficient to bring even the subtlest of traces present at the historical Sankt Vith site to life. Even more, the dense forest caused ‘noise’ in the 3D model. So pretty early on, we decided we needed another solution, which is how we got to knock on the door of Argus Vision.” 

SLAM technique helps mapping process 

Argus Vision specialises in laser scanning based on SLAM technology, as well as the combination of drones and photogrammetry. Argus Vision’s co-owner Seppe Koop: “‘Simultaneous Localization And Mapping (SLAM) eliminates the measuring discrepancy that arises when, in case a conventional, static laser scanner is used, the position of this scanner is changed during the scanning process. The SLAM scanner tackles this issue by applying a computer algorithm that builds a 3D model in real time, ensuring the new position of the laser scanner is calculated continuously. 

This technique is also known as ‘Local SLAM’. Since this type of laser scanning allows for 300,000 points per second to be measured, it can be applied to map highly dense forest areas. In this particular case, approximately 1/5 of the measured points matched points on the actual ground surface. This enabled us to build a terrain model in which one point corresponds to ten cm². Even the slightest difference in height is clearly visible thanks to this technique.” 

Focus on the process

The 300 x 600 meter terrain was measured during two twenty minutes ‘flights’. “The Local SLAM, after descent, is re-rendered using a PC”, continues Jonas Van de Winkel. “This is necessary to eliminate the discrepancy between the start and the end of the scan; a stage we call ‘Global SLAM’. By the way, the longer the actual scanning time, the bigger this discrepancy becomes, so it is best to limit the scanning time to a maximum of 30 minutes. The next step then is to clean the initial point cloud and to georeference it by means of comparison to the digital height map of Wallonia. Lastly, the classification with a split between terrain points and vegetation delivers the final result.”

Hugely interesting result 

The final outcome pleasantly surprised Dr Birger Stichelbaut: “We processed the Argus Vision 3D point cloud using our software for further archaeological research. This gave us a visualisation of the laser measurements in which even small differences in height, 10 to 30 cm, became apparent. In short: the ideal basis to physically reconstruct the Sankt Vith battlefield. The areas where the artillery was set up, the shooters’ hideouts, the small trenches and even the rubbish pits: all of these locations could easily be pinpointed. Our first encounter with SLAM combined with drones has been extremely positive and without any doubt is a technology that opens up new perspectives for archaeological research.” 

Hunger for more

The main asset of SLAM technology using drones is the speed of execution. It takes just a couple of hours to map an entire site. “And in great detail”, adds Dr Birger Stichelbaut. “Even height differences you would not notice at ground level, are clearly visible. Since we look at the site from a bird’s eye viewpoint, we are able to discover links between different locations – even if there is dense forestry around! Thanks to Argus Vision we now know how significant the value is of the Walloon forests with regards to information on the Second World War. These terrains have remained untouched since then. No agriculture, no building activity. SLAM based laser scanning proofs to be extremely interesting to continue researching this area. Which we have all intention to over the coming years!” 

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