By Michael J. Miller, M.A., RPA (Fort Campbell Contractor)
The Fort Campbell Cultural Resources Program oversees the protection and preservation of the many archaeological sites, architectural resources, and cemeteries across the 106,000-acre Installation. Our staff is committed to preserving these resources while ensuring that the Army mission succeeds.
A new way we have begun to document, share, and curate these resources is with photogrammetry. Taking two-dimensional digital photographs and using them as data within a software program, we can create three-dimensional models. Unique features such as State Line Marker No. 20 and headstones from historic cemeteries have been recorded using photogrammetry and then 3D modeled. Select artifacts have also been 3D modeled and curated for the Eastern Band of the Cherokee Indians. We are still working on finding the best way to provide access to these models to tribes, researchers, and public. Looking forward, we hope to record monuments, landscapes, entire cemeteries, and excavations using photogrammetry to enhance public interpretation.
The purpose of this post is to provide guidance based on our experience; we are not experts, but have been successful using an array of resources on photogrammetry.
You’ll find numerous resources on the Internet pertaining to photogrammetry in archaeology. Many of the pages, videos, and blogs portray it as an easy and user-friendly way to document data and model artifacts. This is not entirely the case.
The first step in this process, choosing the right camera, is the simplest. The smartphone in your pocket is likely up to the task. However, if you want to make high-quality models, a digital single-lens reflex camera (SLR) camera with a prime lens (fixed focal length) is necessary. You’ll also need a macro lens for small artifacts. A good understanding of how to use your camera in manual mode is a plus.
The software we use to processes digital images and generate 3D data is Agisoft Metashape Professional. This is a program that uses photogrammetric algorithms to generate 3D spatial data. They offer a 30-day free trial of the software and an educational institution discount but, you’ll need to purchase a license for the software in order to export any models you make. The computer used to run the software and process the data requires certain minimum specifications that are outlined on the Agisoft website http://www.agisoft.com/.
Depending on what you plan to use photogrammetry to record, you may need a photo setup with adjustable lighting, a tripod, a backdrop, a turntable, and scale bars. If your subject is outdoors, a day with cloud cover provides the best lighting conditions. The spacing and location you take the photographs in is very important. In order for the software to tie the photos together they must overlap the subject 40 – 60% and be taken from several angles in a 360 degree spread. Planning your photos is a valuable step that requires time and attention.
Once you are happy with the photos, it’s time to learn the software. The most basic workflow in Metashape is to add photos > align photos > build a dense cloud > build a mesh > apply texture > export model. Learning to use the software will be the most time-consuming part of this exercise. To speed up your learning process, I recommend reading Photogrammetry in Paleontology – a Practical Guide by Mallison and Wings in the Journal of Paleontological Techniques (see link below) as it will take you step by step and explain the software and the workflow in detail for several types of objects and environments.
Sharing the models you make is as simple as exporting the project as an object file (.obj) or uploading to a Sketchfab.com account. SketchFab allows you to share and embed with a free account, although you are limited by monthly credits and if you choose to make models public or not. Many educational institutions have accounts for students and staff.
The proper curation of digital data is an important final step in the process. Original digital photos used to create a model should be kept with the finished 3D model. The pieces that make up the 3D model include the Metashape project file (.psx), a materials settings file (.mtl), an object file (.obj), and the texture file (.jpg, .tif, .png, or .exp), these should be stored together and zipped. Due to the size of these files (large models are often hundreds of megabytes) an external solid state hard drive (SSD) may be the best storage solution.
Is photogrammetry worth all the time and effort? It really depends on your goals, budget, and if you are computer and camera savvy. At Fort Campbell, having the ability to digitize features and artifacts in 3D has proven to be a worthwhile endeavor. The 3D models enhance the viewer experience beyond traditional photos and helps us engage a wider audience.
Photogrammetry in Paleontology – a Practical Guide by Mallison and Wings: https://www.jpaleontologicaltechniques.org/pasta3/JPT%20N12/Pdf/JPT_n012_Jul.pdf
Fort Campbell Cultural Resources Management Program: https://home.army.mil/campbell/index.php/cultural-resources
Disclaimer: This blog is for informational purposes only and does not constitute endorsement by Fort Campbell or the Department of the Army.