During the 2016 Preservation Trades Rodeo, HPTC Historical Architect Mark Slater conducted several sessions on historic building documentation with co-presenters from Vertical Access LLC and the Historic American Building Survey (HABS). Topics ranged from photography to laser scanning and drone photogrammetry.
Documentation in historic preservation is an art and a science. It serves multiple purposes that can play into many aspects of NPS work:
- Planning (at the site, local, regional and national levels)
- Communicating building conservation needs
- Identifying where and when work is completed
- Allowing “virtual tourism”
- Preserving as much information as possible about a structure in case of loss
Drones–Not Just for Spying on Your Neighbors
Documenting places that are hard to get to is problematic. Drone-assisted photogrammetry can significantly augment site documentation. Also known as “unmanned aerial systems” or “quadcopters,” drones took the hobbyist world by storm in the early 2010’s. Attaching a camera to a drone allows the user to take multiple images of a site and later “stitch” them together to create a model. This is an ultra-modern form of photogrammetry—the science of measuring distance from photographs. The practice dates from the 19th century.
Once you start seeing the images created by high-tech documentation methods, it’s easy to see how they they can also be used for interpretation of inaccessible sites. Additionally, extreme weather events such as Superstorm Sandy can wipe out access to the site if not the site itself. In the long term, climate change poses similar threats. The Historic American Buildings Survey (HABS) used photogrammetry to create a virtual tour of Ellis Island incorporating historic photographs and drawings. This tour is primarily of a historic hospital complex not generally open to physical visitation. Virtual visitors can learn how buildings were constructed, and compare their present and past appearances.
Drone photogrammetry’s application is compelling for project work like what we do at HPTC, but also for the gamut of NPS cultural resource management, resource interpretation, and education. The technology brings inaccessible sites within reach (see an example here). Using drones to survey structures also minimizes danger to workers and the public. Images taken by a camera attached to a drone can be stitched into a 3D model using software such as Pix4D. The process is automatic, but the model is manually refined to ensure correctness. Scaled orthographic planes from the virtual model facilitate cost estimation, information storage, and, in instances of damage or loss, reconstruction and/or postmortem interpretation.
But Aren’t They Banned in the Parks?
It’s sort of true; they are banned to the general public. But the NPS recognizes they can play a role in park management.
“Administrative use includes the use of unmanned aircraft by (i) NPS personnel as operators or crew; (ii) cooperators such as government agencies and universities that conduct unmanned aircraft operations for the NPS pursuant to a written agreement; and (iii) other entities, including commercial entities, conducting unmanned aircraft operations for the NPS, provided such entities are in compliance with all applicable FAA and Department of the Interior requirements.”
Remember, if you use drones in the future, commercial drones must be operated by registered pilots. In general, they cannot be used near airports, which are usually located near building-dense urban areas. The FAA is racing to appropriately regulate drone usage. Unfortunately, policy often cannot keep pace with technology development. So make sure your pilot has done their homework on the latest regulations.