up on the street, he used the SX10’s total station functionality to shoot and record the position of each prism. Once inside, they used a digital leveling instrument to collect the height data. Because they weren’t allowed to draw on the floor, they used tape to mark measuring points. Using the established benchmark point as the starting point, they methodically moved along each floor, collecting measurements from the existing walls, doors, and openings and record- ing, on average, 20 height measurements for each floor. To add value to those accurate height data points, Vestbø took 2D DWG files of the building that he acquired from UiB and used TBC to inte- grate them into the finished 2-mm point cloud. Using the georeferenced point cloud, he georeferenced each DWG drawing and then scaled and rotated each drawing so it fit precisely into the point cloud. Through this exercise, they were able to annotate the point cloud showing the correct coordinate and elevation of each height point on every one of the ten floors in the building. Two days after completing the leveling fieldwork, they provided the architect with an updated point cloud layered with the DWG floor drawings and the calculated heights on each floor. “Scanning not only captures all the unique details of the building–– it’s façade, windows, roof structures, and surroundings––incredibly quickly, it provides so much data depth and fea-ture definition that it’s like you’re standing in front of the building or inside it from your own com-puter,” says Vestbø. “A 3D model like that will enable the archi- tects to better evaluate and visualize the structure and incorporate that precise view into their own design model and workflow.” When phase three begins in late 2019 and the interior of the BT build- ing is razed, Vestbø will again return to the site with the SX10 scanning total station to capture the remaining external walls from the inside. Although he can’t anticipate challenges he may face, he is certain that the scanning details will play a pivotal role in transforming such a his- toric icon. And that’s a story he’s happy to help write. Point cloud with integrated 2D DWG files. Each DWG drawing was georeferenced, scaled and rotated to fit precisely into the point cloud, showing the correct coordinate and elevation of each height point on every one of the ten floors in the building. Photo credit: Geomatikk Survey
“Previously, post-processing scanning data could be quite time con- suming because you had to georeference each scan first,” says Vestbø. “With the scanning total station, the point cloud is almost ready when you’re done scanning. It’s a simple, automated process to tie in any unregistered scans and it’s much more efficient.” Automation also played a key role in cleaning up the 3D dataset. Scanning through 550 windows and two different glass roofs created millions of extraneous points inside the building that Vestbø needed to clean and clear. Using TBC’s limit box tool, Vestbø could remove exterior walls to expose the interior data points, and after setting certain parameters and boundaries, the software automatically removed 80 million points of additional data captured inside the building. He ensured the remaining 180 million data points were clean and then finalized the 2-mm point cloud of the building’s façade. For the secondary point cloud, Vestbø also applied the same cleaning tools to remove superfluous features like parked cars and people walk- ing around the building. Three days after completing the phase one scanning fieldwork, Vestbø delivered the precise 3D model of the BT building façade and the sec- ondary point cloud to the architect. Leveling the floors In late January 2019, Vestbø and a colleague returned to the site for phase two of the project: measuring and calculating the height of each of the ten floors in the building. Because of the age of the building, the floors were not constructed with uniform heights. Some floors have slopes, or dips or raised sections with a step––one floor may have all three––which has created not only varying floor heights between floors but along the same floor there could be up to 50 cm (1.6 ft) in height variance. The Geomatikk Survey team needed to accurately survey and calcu-late the elevation levels of each floor to within 0.5 mm (.0001 ft). The crew first established a set of benchmarks for survey control. Vestbø placed a prism on the inside of a window on each floor. Setting In 13 hours of scanning, Vestbø collected 260 million data points. With the aid of TBC software, he cleaned up 80 million extraneous points to produce a clean, as- found point cloud with an accuracy of 2 mm. Photo credit: Geomatikk Survey
MARY JO WAGNER is a Freelance Writer, Editor, and Media Consultant based in Vancouver, BC. She can be reached at mj_wagner@shaw.ca.
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csengineermag.com february 2020
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