We’ve been dealing with some very cool technology lately, both in the field and back on campus. Ben Skolnik, Stefan Woehlke and I presented a paper at the Society of Historical Archaeology Annual Conference in Seattle talking about the costs and benefits one of AiA’s most recent and exciting tools — a 3D laser scanner. During the summer of 2014, we were able to use it to scan our work in the field — in other words, the scanner spins, using millions of lasers to scan the landscape while also taking photographs. Import this data into the computer software and what you have is an interactive re-creation of the landscape, unit, or feature in digital 3D. With this type of data, Ben was even able to isolate one of the girts of a ruined frame structure at SERC and use a 3D printer to create a small-scale model. Below you’ll find an adapted version of our paper, as well as a photos and videos of the process!! After all, this is all about the visuals.
An Intro to 3D Laser Scanning in Archaeology
In recent years, companies such as FARO and CyArk have begun incorporating 3D laser scanners into field-ready packages. Archaeologists have successfully employed these new 3D laser-scanning techniques to record sites such as Mount Rushmore and Merv in modern-day Turkmenistan. Despite the potential benefits of using this technology, which produces quickly scanned, high-resolution images of topography and features, several limitations have slowed it from entering the archaeologist’s standard toolkit. It exceeds the budget of many archaeological research projects and the large quantities of digital data recorded by these machines (often millions of points) present challenges in both manipulation and curation of these datasets. Additionally, methodologies that incorporate these scanners as a part of excavation remain undeveloped. This paper explores the use of a 3D laser scanner by Archaeology in Annapolis at several sites, and offers an evaluation of its successes and shortcomings as a tool to aid archaeological excavation and research.
Archaeologists have frequently turned to new and innovative technologies to assist in the excavation, recordation, and interpretation of sites. Radio-carbon dating is perhaps the most profound example of a technology that has fundamentally changed the discipline; but there are many other tools and methodologies that have been developed that assist us in digging up the past. As the cost of terrestrial LiDAR systems comes down, we expect that it will be used more and more frequently as a part of the archaeological toolkit.
Terrestrial LiDAR, also referred to as 3D laser scanning, uses active pulses of laser energy to create a detailed three-dimensional digital model of a mapped surface. The instrument sends out a pulse of light in the [range of the spectrum] at a known angle. That light energy travels along that specific trajectory until it encounters some physical object in its path. Upon hitting this object, some of the energy is reflected back to the instrument platform. The scanner records the time it took for the laser to make this round trip as well as the intensity of the energy returning. Because we all known the speed of light (…299,792,458 meters per second, in case you need a reminder!) , we can take the time it took for the signal to return to the sensor, divide it by 2 (because it had to go there AND back), and divide by our speed to get the distance between our sensor and the point we just mapped. We can now change the angle at which our laser leaves the scanner and map another point. If we repeat this process millions of times, we end up with a digital model of the surface we just mapped. If you’ve ever spent time in the field, you’ll know how long it takes to map by hand, or even using a total station and prism — this process not only does all of this in a fraction of the time, but records everything, including exact distances.
Using the 3D Scanner at Wye House and SERC
Excavations at Wye House in Talbot County demonstrate the value of using 3D scanning to record contexts in situ as they are excavated. This deposit was located beneath what was once the entrance to a brick slave quarter on Wye Plantation. The context, which consisted of a number of circular objects laid carefully beneath the entrance – including colored, white, aqua, or metallic artifacts that mediate the watery barrier between the living and the dead in African spirit practices. This type of deposit must be carefully mapped and recorded prior to and during each stage of its removal – and this is where 3D scanning is a particularly valuable resource. Using the scanner, millions of points were collected that allow for the deposit to be reconstructing digitally, preserving exact locations and measurable information that would normally take hours or days to record by hand. Another benefit to using the 3D laser scanner at this site is the opportunity for community engagement with archaeology. To put it bluntly, it’s a cool technology. At Wye House, members of descendent community came out and watched as Ben gave a demonstration of the scanner, and were fascinating by how ‘high-tech’ our terrestrial excavations had become. It regards to generating public interest and creating a visual product that can communicate the archaeology to a wide audience –point clouds are not only aesthetically interesting but interactive – 3D laser scanning holds a lot of potential.
During the 2014 field school at the Smithsonian Environmental Research Center, Archaeology in Annapolis conducted testing around the extant remains of a late 19th century frame building, likely a tenant house for the Sellman Family Farm in Edgewater, Maryland (previously a slave-holding plantation). Now a part of the SERC campus, the wooden frame of this structure forms a visible ruin on the landscape – albeit a delicate one, as the wood has been subjected to decades of the elements. Many of the components of the structure, including beams, girts, a fallen chimney, and brick piers, lay relatively undisturbed where they have fallen, and present the opportunity to imagine a reconstruction of the building through their careful recordation. Our archaeology focused of the exterior of the structure so as not to disturb the fragile ruin, with test units in the front, back, and side yards, but the 3D-laser afforded us the opportunity to record what was left of the tenant house in a level of detail that drawings, maps, and photographs wouldn’t have captured alone. With millions of points taken and stitched together, the structure can be rotated, zoomed in on, and explored in full 3D on a computer. Further, one of our team [Ben, I’ll give you credit for this] was able to isolate one of the architectural elements from the structure – the long girt along the east [right?] side – and import it into MeshLab, allowing us to use 3D printing technology to recreate a small scale replica of the piece. With further work, the potentials of this type of technology in archaeology present the means to recreate high-detail and 3-dimensional models of archaeological sites at every stage of excavation, both digitally and physically.
The Costs and Benefits
There are many benefits to having a tool like this available at an archaeological site like the two described above. One is the ability to map things quickly and accurately, as we discussed in the intro section above. This type of technology records sites and contexts so well that you would be able to go back and look at an entire context in situ, and interact with it digitally, even after it’s been removed. (Never forget that excavation is a destructive practice — once something is taken from the ground, it cannot be put back, which makes recording one of the most important parts of our process!) Another benefit is the potential for community engagement — exciting technology gets people interested, and is a great way to engage people of all ages at an archaeological site. Beyond that, the images produces are both interactive and beautiful, and provide the potential for things like 3D printing. These are the types of products that can be used in archaeological education, museum exhibits, community outreach and online resources.
There are some drawbacks to 3D scanning as well. The main obstacle is price — it is a very expensive piece of equipment, and not all archaeology projects can afford it. Even our scanner, which was the entry model from FARO, was an expense that we shared with our School of Architecture at the University of Maryland, College Park. It is important to understand that in addition to the cost of the scanner itself, there are other associated costs to keep in mind. Computers, data storage, software licenses and training must all be factored into the budget for a 3D scanner. Another drawback is the size of the data, which requires high processing power and a lot of space for storage. Working with these datasets can take a lot of time, depending on how fast your computer is (and some computers can’t handle it at all!).
As the cost of terrestrial LiDAR platforms comes down, it is almost certain that they will be used more and more frequently in archaeology. This means that archaeologists will need to develop good methods for using them in the field. As they enter our toolkits, we will need to think more about how best to use these scanners to the benefit of archaeology and the communities we work with!