One of the limitations I often face when using 3D technology for public outreach is the still very small database of models to pull from. The process for creating a 3D model of an artifact or site is time consuming and most of us simply do not have time to model everything we would like too. Therefore, it is in our best interest to find ways of making 3D technology more appealing to our peers in other branches of archaeology. For this post, I tested the CloudCompare software and found that it has a lot of potential.
Testing the Program
Recently, the American Civil War monument that I used as a subject for my first photogrammetry model was knocked over. The Sons of the Confederacy group here in Tallahassee, Florida believe that it was accidently hit by a work vehicle and was not intentional vandalism. I saw this as a perfect opportunity to test out CloudCompare and see what changes might have occurred to the monument.
The CloudCompare software overlays the point cloud you get from either photogrammetry or laser scanning the original model
on another version
to get a very nice visual comparison of the two. This is the first version using CloudCompare:
Note the blue in the center of the monument, indicating little change, and the red edges, suggesting a lot of change. For this first comparison, I aligned the base and this revealed that the marker’s position had changed (it is now set more square than before). This is something that I had missed while photographing and looking at the models separately. If you click on annotation 3 we can very nicely see the new footprint for the marker on its base. This also might explain why I could not get CloudCompare’s auto-alignment feature to work like I was expecting.
Also in this comparison you can see the two large chips (marked by annotation 1) that were removed from the base. While these show up, comparing the base is problematic as the original model had a lot of grass growing right next to the stone, and the recent version has the glass cleared away. This resulted in a lot of false positives when looking for damage on the base.
Since it was the marker that was knocked over though, I really wanted to see how that had changed. After aligning the face of the models, I got some more interesting results.
The first thing you might notice is that the top edge of the plaque and the edge of the oval on the plaque are red. I suspect that what we are seeing is one version of the models not generating this edge very well.
Annotation 2 highlights another piece of damage that I had previously missed in the form of a new notch in the marker’s edge. If you look back at the new version of the completed model, these notches look pretty uniform and this marker has been moved before. This makes me wonder if the equipment used to hoist the stone is causing this damage.
Also note that the cosmetic damage to the plaque does not show up. I was hoping that the program might track color changes as well, but you cannot have everything. Also, a chip missing out of the top-front edge that is not highlighted as much as it probably should be. I suspect some fiddling with settings should make this pop out more.
As a test, this monument was the perfect subject. I saw the changes that I expected to see, saw changes I had missed, and learned about some of the limitations of CloudCompare. The potential for this program as a research tool for documenting sites and artifacts is pretty obvious. However, I see a more direct use in our public outreach programs as well.
In particular, the Florida Public Archaeology Network has a program called Heritage Monitoring Scouts where we are organizing public volunteers to help monitor coastal sites that are threatened by sea level rise. If we were to train certain volunteers to take pictures for photogrammetry purposes, we could use CloudCompare to help document the degradation of these resources over time. This would be very useful information and I suspect that participants would find it rewarding as well.
Any other ideas? How would you use this software?
Tristan Harrenstein is trained as an archaeologist and has a passion for outreach and education. This is fortunate as he is also an employee of the Florida Public Archaeology Network, an organization dedicated to promoting the preservation and appreciation of our archaeological resources. He shares a blog space with his boss (Barbara Clark) and you can read more blog posts on other archaeology related subjects that tickle our fancy here.