Of Abe And George

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On October 7th, 2014, Steven Schorr, President of DJS Associates, Inc., a forensic consulting firm based in Abington, PA, ceremoniously added two completed projects to the "Ark" as part of the 2nd annual CyArk 500 Summit, held at the National Archives in Washington, D.C. Ben and Barbara Kacyra, Founding Directors of CyArk, presented the glass project plaques to Steven, who was joined by Robin Nixon of the National Park Service (NPS), and Richard O’Connor, Chief of Heritage Documentation Programs at National Park Service (NPS).

The two projects? The Lincoln Memorial and the Washington Monument. In December of 2013, we began the first of the two projects, the Lincoln Memorial, by traveling to Washington D.C. from Philadelphia to get a first-hand look.

The Lincoln Memorial
While a combination of aerial map imagery and simple online image searches provided us with plenty of visual information on the public and exterior portions of the memorial, the coordinated site visit allowed us access to restricted, more mysterious portions of the site, including a massive basement, along with the attic and roof areas.

A look at the basement revealed two levels: a mezzanine walkway traversing the perimeter of the building, overlooking the lower basement. The basement as a whole was quite a bit larger than anticipated, and with many columns, appeared it would require a significant number of scans. A narrow winding stairwell provided access to the attic and roof levels, where we discovered that specially trained personnel would be needed, in order to comply with OSHA regulations regarding harness use. The attic, in particular, was an area where personnel safety would be top priority.

With all of this information gathered, we began to plan our approach to document the site for the purposes of digital preservation, enhancing education programs, and providing a baseline three dimensional model for site management. To meet these goals, we set out to achieve five millimeter point density throughout the site.

Time restrictions dictated that we would need to operate multiple terrestrial scanners concurrently, utilizing two time-of-flight Leica C10 scanners for the exterior and main chamber work, and two phase-based Faro Focus 3D scanners for the interior and underground portions. The C10s provided great reach, while maintaining high point density, which made them well suited for the exterior work. Conversely, the Focus 3Ds offered superb portability, coupled with low scan times, making them a great option for the interior work.

In the public areas of the site, the sheer number of people who visited the memorial throughout the day presented a challenge. While largely unavoidable, we did complete our scans in the main chamber and on the steps in the early morning hours, giving us the best opportunity for low noise scanning.

In the main chamber, we also considered and executed a plan to gather data on the upper portions of the Lincoln Statue. To accomplish this, we made use of an aerial work platform, which allowed us to scan from a height of 35 feet, capturing the upper arms, legs, and top of old Abe’s head. This data would prove useful for "fill in" data. Due to the swaying motion of the extended boom, the data collected was less reliable than data collected from ground level.

The most challenging portions of the Lincoln Memorial scanning took place in the massive basement, where hundreds of concrete columns rise up from a dirt floor, some forty feet, to support the weight of the main chamber, marble and limestone above. With so many columns, the basement required precision in planning and hundreds of setups in order to maximize the scan coverage. Another challenging area in the basement was the portion directly beneath the steps, where the ceiling slowly encroaches above, in the end being just ten feet from the ground as you make your way towards the Reflecting Pool. This portion of the Memorial had a distinctly different feel than the rest of the basement, with its stalactites and standing pools of water which were remnants from a recent rain. These water pools, coupled with the low ceiling, made finding suitable scanning locations a bit more difficult, taking more time.

The Washington Monument
When planning for the Washington Monument, one of our main concerns was getting quality data on the upper portions of the obelisk. We had initially hoped that we might be able to collect data by use of an unmanned aerial vehicle (UAV), but quickly came to the realization that there would be no "drones" flying in the heart of our nation’s capital. Another option that was considered was the idea that we could have a crew rappelling from the top, using a special scanning rig. In the end, we combined our efforts with members of the Heritage Documentation Programs at NPS to perform ultra-high density scans from ground level, using a C10.

As part of the planning process, we again made the trip to DC to inspect the conditions of the monument first-hand. Inside the Washington Monument, lining the walls of the stairwells, are some two hundred memorial stones, each with its own significance. That being the case, we planned accordingly to capture the stones with as much detail as possible. A special "elevator" tripod was used on certain landings, to ensure that we could collect relevant data on the memorial stones that reached above our heads. We also made use of our Artec Eva, a structured light 3D scanner, to collect measurements on some of the more detailed stones.

Another variable for consideration when scanning the Washington Monument was the fact that there are not many "unique" features surrounding the monument. Targeting would become critical to combining scans taken from the open "field" areas surrounding the site. As such, we deployed numerous specially-made targets around the site. This, and the timely release of Leica’s Cyclone 9.0, allowed us to register all of the exterior data with relative ease.

Inside the monument, on the observation level, much of the supporting structure is cased in glass, which meant that "noise" would be higher in these areas. Since we had a small window of time in which to scan these areas, we made a decision to forego the lower noise, longer scan option, in favor of faster scans, and more time spent in post-processing dealing with the additional noise.

One of the most interesting items at the WAMO site is the "mini" monument. A thirteen and a half foot replica of the Washington Monument, the mini monument is located just south of WAMO’s entrance, safely hidden underground. Built in 1898 by the Coast and Geodetic Survey for the purpose of computing settlement records for the monument, this replica is now sheltered by a standard manhole cover, with thousands of people passing by it daily, never knowing it is there (unknown, 2014). Using an inverted Faro Focus 3D, we took a few scans of this concrete obelisk, including it in the larger "site" point cloud.

In all, between the two sites, we scanned from nearly one thousand unique positions, collecting nearly ten billion data points. It was a one-of-a-kind experience, and we were able to explore and document the sites as few have done before. As for the future, we are working closely with CyArk, the National Park Service, and the Heritage Documentation Programs at NPS to scan the National Mall in its entirety. This work will eventually result in one large, comprehensive dataset that will serve a multitude of purposes for years to come, including educational content, and virtual tourism. I look forward to the challenges that lie ahead, and to carefully documenting more of our national monuments, allowing the rest of the world to see them as I have.

Works Cited
unknown. (2014). List of Classified Structures. Retrieved 10 20, 2014, from http://www.hscl.cr.nps.gov/: http://www.hscl.cr.nps.gov/insidenps/report.asp?STATE=DC&PARK=NAMA&STRUCTURE=&SORT=&RECORDNO=5

Jon W. Adams, Director of Architectural and Heritage Services with DJS Associates, an Abington, PA engineering firm, was the project manager for the digital scanning and preservation of the Lincoln Memorial and handled the technical aspects of the project including planning, data collection and processing.

A 6.020Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE