Tunnel Business Magazine

OCT 2018

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weekends during two survey campaigns totaling about six full weeks of underground fieldwork. The team alter- nated between underground and above ground, where they performed survey loops for geo-referencing and col- lected scans of the cityscape to provide context to the under- ground structure. They completed up to 63 scans per day and captured panoramic photos to color- ize the point clouds. Scanning began in one quarry and pro- gressed day by day to the end of another quarry. Once these scans were captured, the stu- dents moved to other areas of the subterranean network. Scans were initially processed in RealWorks for registration and georeferencing. Back at the hotel, they pre-processed the day's data to ensure it had been collected properly. The Wellington quarry is a museum open to the public, so the students sometimes had to work around public tours. The pilot survey started right . 13, 2015, Paris terrorist attack, however, so most tours in the tunnels were cancelled and scanning in the museum was given prior- ity. The speed of the TX8 was phenomenal, Sirguey said, and the ability to use it with an SLR camera was critical to the team's progress. Over the course of the proj- ect, the team completed near- ly 1,000 scans using mainly the Trimble TX8 scanner, col- lecting about 100 gigapoints (100 billion points), making it one of the largest scanning projects of its kind processed in ealand. The final resampled point cloud at 2mm spacing is about 25 gigapoints. The control network was es- tablished for the tunnel and quarries but teams extended it to the outside so they could get goo tic positions and tie it to the regional grid. In addition to the scans, 9,768 high-resolution photos were captured and processed into 814 panoramas. A georef- erenced network of 32 control marks, including outside and underground marks, was sur- veyed with sta total stations. Closed traverses were used to carry control through the tunnels, and the network of observations was adjusted via least squares es- timation. Scan data was pro- cessed in RealWorks to create a variety of digital data prod- ucts, including raw scans; full scans that were registered, colored and georeferenced; a resampled point cloud at 2 mm between each point; and photo panoramas. Sharing History Shortly before the project was complete, Sirguey and his team were invited to at- tend the remembrance cere- mony of the Battle of Arras in France and present the find- ings of the project. They shared details of their work and unveiled the latest animation of the un- derground network data- set. The team also generated a fly-through inside the 3D point cloud, exemplifying the full extent of the completed survey (available at youtu. be/0DkPwl25dC4). To generate the fly-through, Sirguey had one of the stu- dents create a number of "rush" animations of various sizes. Sirguey determined the speed and renderings. It took about two weeks to clip and mount the rushes together with music to form a narra- tive. The fly-through was later gifted to the museum. Additional animations and navigable 3D models were created for museum and pub- lic use (see www.otago.ac.nz/ lidarras), and a 3D model has been archived as a digital re- cord to ensure the many at- tributes of the structure are protected, including parts at risk of being lost through de- teriorating chalk or alteration of tunnels due to urban devel- opment. The Work Continues The project didn't end with the commemoration. In sum- mer 2018, a regional agency conducting an inventory of tunnels in northern France approached Sirguey about his work at Arras. The agency had heard about the success of LiDARRAS and asked for as- sistance in producing a "light" resampled version of the point cloud, as well as a footprint of the area scanned to contribute to its inventory. "This is precisely the out- come we anticipated," Sirguey said. "It's pleasing to see how the project is contributing to other projects already." Sirguey and his team are now in discussion with the Zealand tional Library about archiving the results. In addition, the Toitu Otago Set- useum, an early part- ner of the project, has invited them to give a lecture in the context of exhibitions of the World War I battles. "LiDARRAS went beyond what we ever expected," Sir- guey said. "The data and im- agery were excellent, and we had everything documented and turned over to the city of Arras in time for the anniver- sary. But beyond its technical and historical merits for the general public, the project of- fered a unique opportunity for academic collaboration between Franc Zealand to preserve a piece of history, as well as sharing sur- veying education across gen- erations and cultures." TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // OCTOBER 2018 A screenshot of the TLS data showing high density and resolution of the data captured. 3 4 F E AT U R E S T O R Y

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