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By Lee J. Nelson
Scanners fire a laser beam at solid facades. The light that bounces back contains x-, y- and z-coordinates: the position of the specific points in space, their respective red, green and blue intensity values, together with surface reflectance properties. Terrestrial laser scanning records data in digital format to sub-centimeter precision. By contrast, airborne LIDAR collects so-called “point clouds” with about 1-meter accuracy.
Laser scanning is a line-of-sight technology; it only documents what it “sees,” although, to build an accurate picture, a given point cloud can incorporate scans from many different locations. The modality does not return sub-surface or surface-penetrating information. With Leica’s dedicated Cyclone software, users can manipulate the data to generate traditional 2D CAD, panoramic imagery, video animations and 3D models. All are stored in centralized and redundant databases. Dissemination to the public is via a browser-based portal. This fulfills not only the demand for open access but also serves educational purposes and cultural tourism.
At Mount Rushmore, the Leica equipment collected more than 50,000 dimension points per second, representing the first highly accurate and comprehensive survey of the mountain. To accomplish that, researchers had to approach as close as 10 mm (0.39 inches) from the monument’s surface, a particularly onerous task, given the 5,725-foot (1,745-meter) altitude. During their first week on site, the team successfully chronicled the interior and exterior of the renowned Sculptor’s Studio, the Hall of Records and several other perspectives. They set up workstations behind the sculpture and along the Presidential Trail to get the top of the heads as well as the front of the faces.
“The size of the monument and the surrounding irregular terrain were some of the unique challenges...” said Douglas Pritchard of the Glasgow School of Art’s Digital Design Studio. “We expect[ed] to get complete contours of the presidential faces and surrounding rock faces and the talus slope and vegetation down to a sub-centimeter level of accuracy. In addition we will have complete geo-referenced photography.”
Image processing is time- and labor-intensive and entails merging all the separate scanned locations, matching data points, confirming accuracy, assembling renderings and overlaying texturing to achieve photo-realistic perspectives and animations. The group’s work persists. And, as Pritchard anticipated, will continue over the coming months and years with the objective of advancing digital preservation and programming for the Park Service’s preeminent Mount Rushmore National Memorial. AI