Chris Albon and Juliana Fernandez check on their timelapse of the shoot.
Last week two members of the CoDA team (Michael and I) had the unique opportunity to work with one of the masters of the art and science of photogrammetry, Tom Noble, whose excellent manual I reference below. He’d probably see a lot of things that need correcting in what I’m writing. Tom works with the Bureau of Land Management in Colorado, and has participated in such exciting projects as the brief uncovering of the Laetoli footprints in Tanzania at the beginning of this year. We were joined by two faithful interns of the Presidio Archaeology Lab, Chris Albon and Juliana Fernandez, who worked to create a timelapse of the two-day shoot.
What is photogrammetry? It is a method for reconstructing three-dimensional data from scientifically taken photographs for the purposes of laboratory analysis. It is especially useful for that most destructive field of which we are so fond — archaeology. You’re familiar with 3D movies, I take it, and the process is somewhat similar. If you’ve ever watched a 3D movie without your glasses, no doubt you’ve noticed that what you are actually seeing is two overlapping images of almost the same framing. When you wear the special glasses, your brain is tricked into sensing perspective and you perceive the flat projected image as having dimension.
With scientific photogrammetry, this process is replicated with software. You take two images with overlapping subjects (ideally with more than 50% overlap) and run them through some software that generates 3D data from pixels by aligning matching points in the two images. This is called stereophotogrammetry. And, if you are like us, and you have software that can calculate series of stereophotos, than you can cover a large amount of area in high detail. If you begin to include calibrated scales and points, such as objects with known measurements and points surveyed with total stations, you can generate 3D models that allow for virtual measurement with sub-millimeter accuracy.
Compared to methods like laser scanning, photogrammetry is a much more accessible and cost-effective option for those with such challenges as poor funding or unconventional subjects. Photogrammetry is applicable for collections of tiny artifacts, small, confined spaces, and hard-to-reach or sensitive subjects, like the footsteps at Laetoli, or, traditionally, moving aircraft. All you really need is a good(-enough) quality camera, the appropriate software, and a mixture of proper methodology and experience. Obviously, the quality of your product will increase in direct proportion to the quality of the combination of these variables.
I fiddle with cables while Tom plots his course of action
At the Presidio, we were working on the exposed original adobe walls of the Building 50, or the Officers’ Club, which is currently undergoing extensive renovation. We, along with the archaeologists of the Presidio Archaeology Lab, are some of the only people who have the privilege of seeing the original structures as they stood over 200 years ago. The products of our effort will allow future visitors to engagingly interact with and virtually explore what will lie beneath the new walls, in addition to providing a new repository of information (we collected almost 70GB of raw data, not to mention the potential size of the processed content). Stay tuned!
Resources
Best photogrammetry software for your buck (if you’re somehow academic :-/ )
What you’ll buy when your team gets big government money