3D mapping project reveals hidden underwater wonders of South Australia's Limestone Coast

The patchwork of caves and sinkholes on South Australia's Limestone Coast is an underwater wonder most people will never fully experience.

But a project using cameras to create 3D maps of the region's major sites hopes to give the public a glimpse of the caves that weave below streets and houses in Mount Gambier.

Advanced cave diver Will Passos, with assistance from fellow members of the Soggy Wombats dive team, has used photogrammetry and computer software to recreate these dive sites.

"With photography being an interest [of mine] … this idea came about using photogrammetry to try and map them," he said.

"There are old and good maps that people have been doing for the past 40 or 50 years, but it's been a while since anyone updated those maps.

"We did a trial at Allendale [East], just with a big camera and not enough lights, and it was a great result."

Since that first trial, the method has been refined and resulted in models of a number of sites, including Pines and Iddlebiddy caves.

Mr Passos now uses four action cameras, each taking a photo every second, and plenty of lights to ensure the model is as accurate as possible.

With a scan of the Engelbrecht Cave in the heart of Mount Gambier now complete, Mr Passos said he wanted to show people how the passages wove under the city's streets.

From primitive to high-tech

In the early days of caving in the region, mapping was a difficult task.

Ian Lewis, who has been diving for about 50 years, said the mapping efforts were a response to tragic deaths in the region.

But he said early efforts were "primitive", using adapted surface mapping techniques underwater.

"We'd take [measuring] tapes underwater, we had underwater compasses on our wrist, we had little waterproof notes that you could write on with a pencil underwater," he said.

"We drew them out on graph paper and measured the angles that we'd recorded from the compass and then started drawing in the edges of it.

"These are similar techniques that they use to map the dry caves at Naracoorte, where the fossils were found, but it's just a bit harder underwater."

Mr Passos said he was similarly adapting techniques from other applications.

"Photogrammetry is well known. The construction industry uses point clouds all the time … so it's not groundbreaking technology, it's been there for 100 years," he said.

"The application is a little bit different, and the fact that it's underwater makes it even a little bit more different.

"Not everyone is willing to take a bunch of cameras to go underwater instead of diving to record things.

"I would say there is a trend globally for divers that are involved in cave diving to do that because it's just not us that realise that there is a gap and that we need more information."

Greenfield for exploration

The maps the team has created are now being actively used by divers, with the information available on the Cave Divers Association of Australia website.

But Mr Passos said he also thought about how the modelling could be used to better inform the public, including animations or videos.

"The models are really heavy because they're very detailed, so it's always a question of finance."

The modelling has also already led to the discovery of an extension at Pines Cave, near Tantanoola, after investigating part of the model that did not close.

"The scans helped us try to identify where to look, which is a great thing," Mr Passos said.

"We didn't think that we could get that sort of insight from the scan."

Mr Lewis said he was excited to see what the technology enabled.

"Will [Passos] and the others are really at the cutting edge of all of this," he said.

"It's fantastic what they're doing."

Mr Passos said he wanted to look further afield for how this technology could be used, including on unmapped caves across Asia.

"When you go look overseas, like Thailand, Laos, even Japan, there's nothing," he said.