Documenting Architectural Facades with the Laser Scanner LS

Feb. 24, 2009

Renovating historical landmarks requires a careful balance between preserving the architectural elements that characterize the generation of the original build while updating items to support modern life. Thus was the burden consultants faced when designing plans for a $30 million restoration of the Northwestern Mutual Life building in Milwaukee, WI.

Constructed in 1914, the Marshall & Fox-designed neoclassical building on Wisconsin Avenue boasts ten 74-foot high, 422-ton columns with Greek Corinthian treatments, and is crowned by a majestic granite cornice. Restoring the cornice was key to the historical preservation of the building.

Having been built before the age of computers and CAD programs, the first step of the restoration required obtaining digital as-built documentation of the cornice. Local consulting firm, SightLine, LLC, was charged with the task of gathering the measurements from the center points along the cornice of the building.


Bridging the gap between innovation and tradition, SightLine utilized Laser Scanning technology to generate the measurements necessary to restore the classic beauty. Sightline collected the measurements with the FARO Laser Scanner LS 880.

“The FARO scanner was chosen to perform these scans because of its ability to scan from a significant distance and produce accurate data,” said SightLine president Penny Anstey.

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The Laser Scanner LS builds a 360 degree point cloud of a scanned surface by sending an infrared beam into the center of a rotating mirror. Using encoders to measure the mirror rotation and the horizontal rotation of the Laser Scanner, the X,Y,Z coordinates of each point can be registered and modeled.

Sightline completed the survey of the cornice in four days. The Laser Scanner afforded Sightline the luxury to safely collect the scans 150 feet away, within an accuracy of 1/8 in. All measurements were completed without erecting any scaffolding or dropping swing stages over the side of the building.

“Almost all of the data was collected from the ground,” Anstey observed. “The contractor seemed to think the equipment was magic because it could produce a point cloud view as fast as it was being scanned.”

Sightline overcame any line-of-sight issues by strategically placing registration spheres or targets around the scanner and the building. The scans were taken from different viewpoints on the ground and roof top and linked by the spheres within the Scene software.

The clear-view representation of the linked information produces a visualization similar to that of an x-ray. The effect left the contractor with the impression that the Laser Scanner LS could scan through walls.

Sightline selected portions of the 3-D point clouds, and through viewing the cloud in various directions, they traced the items in AutoCAD Architectural Desktop to generate line drawings. They produced 16 sets of digital 2-D drawings of the cornice and building profile. The scans revealed that the original design drawings did not match what was actually built. An entire wing of the structure extended out further than the other, something that was not noticeable to the human eye.

Once the contractor saw the detail generated by the scans, he requested additional information about the building. Sightline provided elevation studies and details on sections through typical areas (such as window bays) and ornamental architectural elements. More deviations were discovered. While the existing drawings documented finials as stylized acorns, the scans revealed that they were actually barley hops.

Sightline was able to provide the information without revisiting the actual site, due to the immense amount of data collected during the initial scanning. The Laser Scanner LS captures 120,000 measurement points per second, therefore, generating the additional information was only a matter of software management.

“We feel that laser scanning has an endless amount of potential and would benefit anyone in time savings, error reduction, and added safety,” stated Anstey.

The rapid rate of collection, ease of data capture, and accuracy of measurements were major factors that influenced Sightline to employ laser scanning techniques versus traditional survey methods.

“Using the former method to gather measurements could have taken months, considering that a large amount of scaffolding would need to be erected,” stated Anstey. “Not to mention the fact that if workers had missed anything, they would have to keep going back to the site to collect data. And who is to say that the data would have been accurate?”

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