Bringing a shipwreck back to life with photogrammetry
A little over 76 years ago, the British merchant steam ship SS Thistlegorm was sunk by a WW II German bomber off the coast of Egypt, taking nine souls down with it. It has only been seen in detail by divers, but a new website from the University of Nottingham and Egypt's Alexandria Universities lets you experience the shipwreck via immersive 3D models and 360-degree VR videos.
The underwater photogrammetry study is one of the first to use 360-degree, 3D video. Divers carried 360-degree Kolor GoPro Abyss rigs, each with six individual cameras shooting 4K Ultra HD footage. To create a 360-degree virtual "guided tour" of the ship (below), the team mounted the Abyss system on the front of an underwater scooter. Each dive captured 50GB of data, for a total of 1.5TB of footage.
"For me, 360 video is a big step forward as it recreates the diving experience," said University of Nottingham project director Dr. Jon Henderson. "You can get the impression of swimming over it and through the internal parts of the wreck."
To build the 3D model shown at top, the team took over 15,668 images to capture the external model of the ship and seabed, along with 11,164 interior images for the deck, holds, captain's cabin and other areas. It took 65 days of continuous computer processing to build the five survey models.
The wreck is one of the world's most popular scuba sites, which has created a somewhat urgent need to preserve it digitally. "Aside from looting the main issue we have is a lot of the dive boats that go out there are actually mooring on to the wreck itself because there is nowhere else to go," Henderson said. "We have seen some boats tying on to more fragile areas, including the guns, the bridge and the railings -- which can cause damage."
The Thistlegorm survey is part of Presence in the Past, a wider archaeological study financed by the UK's £735 million ($970 million) Newton Fund. It was also created in cooperation with UNESCO's "Rising from the Depths" underwater preservation effort.
"Nine men died on the SS Thistlegorm, five Royal Navy gunners and four merchant sailors, just a small part of the 35,000 out of 135,000 Merchant Navy sailors that gave their lives during the war," Dr. Henderson said. "In the Merchant Navy one in four men did not come back – that's the highest proportion of all the fighting forces."
