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Yongala 3D wreck photogrammetry

The SS Yongala sank in 1911 during a cyclone near Cape Bowling Green in the central Great Barrier Reef. The wreck is about 100 m long lying on a flat seafloor in 26 m of water. The Yongala is one of the world's top dive destinations as the wreck provides a complex habitat for prolific marine life.

yongala photoscanYongala 3D wreck in PhotoScanWe have been experimenting with underwater photogrammetry over the wreck, stitching together multiple overlapping photos using Agisoft PhotoScan software to create an orthmosaic of the complete wreck. Julia Sumerling, a renowned underwater photographer, captured the photos during May 2015.

Photogrammetry, or Structure from motion, is a range imaging technique for estimating 3D structures from 2D image sequences. The PhotoScan software first aligns the photos with sparse matching points, then creates a dense point cloud from the aligned photos.

Ground control points from multibeam sonar were used to map prominent points on the wreck into their correct geographic postition. A mesh was then created over the dense point cloud, leading to a digital elevation model with 1 cm resolution and an orthmosaic with 5 mm resolution.

Outputs also included a Wavefront obj file of the mesh and texture, and brought into Blender 3D computer graphics software for generating a 3D model of the wreck. The Blend4Web add-on in Blender was used to export a WebGL html file of the wreck for viewing the wreck in 3D through a browser.

A 5 cm resolution Google Earth kmz file of the wreck and WebGL html file can be downloaded below.

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