Advanced Imaging

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Advanced Imaging Magazine

Updated: January 12th, 2011 09:49 AM CDT

A Monumental Task

An imaging project is designed to help save the iconic Mount Rushmore from the effects of weather, physical erosion and more
The classical view of Mount Rushmore. Carving of the monument by Gutzon Borglum began in 1927 and was completed in 1941. Although jurisdiction over Mount Rushmore was ceded to the Department of the Interior's National Park Service in 1933, nearly 50 years passed before general acknowledgment of the necessity for preservative action.
Amy Bracewell, National Park Service
A Technical Ropes Team works with a custom-made tripod to acquire detail of the Roosevelt sculpture’s eyes.
© National Park Service; photo by the Kacyra Family Foundation/CyArk (Oakland, Calif.
By scanning the faces millions of data points are collected to create a highly accurate digital record of the monument.
© National Park Service; photo by the Kacyra Family Foundation/CyArk (Oakland, Calif
Separate laser scans are combined to generate a rendering of the Jefferson sculpture.
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By Lee J. Nelson
Contributing Editor

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



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