Friday 11 December 2020

4D in archaeology: 3D documentation VS 3D reconstruction

 Hi everybody,

On 23 April 2020 I was asked by my friend Piergiovanna Grossi to give a lesson about 3D and archaeology at the University of Verona. Unfortunately I cannot share here this lesson (at least not yet), due to some restrictions. Nevertheless I would like to write a fast post about one of the topics that seem to have surprised the students: the difference, in archaeology, between 3D documentation and 3D reconstruction.

To keep it simple (KISS principle) we have to consider that we can define our reality (at least in a simple way) in 4D, through three spatial dimensions (x,y,z) and a temporal dimension (t). For this reason, when we work on an archaeological project (excavation, survey, etc...) and we want to document something, we have to pay attention that we are not simply registering the data in 3D, but we are doing a digital copy of the object of our investigation, during a specific time lapse, so that we are recording his physical aspect (morphology) as it is at the moment in which we are working on it. In other words, we are recording a 3D of the object as we see it now (but it would be more correct to say that we are recording it in 4D: x,y,z and t). This is what we call archaeological documentation, but we have to keep in mind that the object as we see it can be very different from the shape it had in the past (like the ruins of a castle are different from the castle itself). Moreover we have to consider that a single object may have had various shapes in the past (a castle could be the result of various architectural stages). This is lead us to the main difference between an the archaeological documentation (which record the object as we see it when we study it) and the archaeological reconstruction (which tries to rebuild the original shape of the object in the past).

This difference is important also because, in Digital Archaeology, 3D documentations  and 3D reconstructions are performed with different kind of software. In the first case we can use SfM-MVS techniques with FLOSS like MeshRoom, OpenMVG, etc..., while in the second we use 3D suite like Blender, even if, recently, Cicero Moraes wrote an add-on able to join this two aspects into a single application: OrtgogOnBlender.

Of course, working in Arc-team together with Cicero Moraes, it is obvious for me to mention him for this topic, but this is due not only to his effort in developing OrtogOnBlender, but also because, in order to explain the students this fundamental difference between archaeological documentation and reconstruction, I found out that the best way was to  show the some example of our past projects related with Forensic Facial Reconstruction (FFR). In fact I started showing some example regarding the medieval of Torre dei Sicconi and the roman site of Villa di Valdonega, like the image below...


The Roman site of Villa di Valdonega: 3D documentation (up) and 3D reconstruction (down)

... but suddenly everything was more clear when I showed an example of FFR, like this one:


The FFR of St. Valentine of Monselice: on the left side the reconstructive model, on the right side the documentation of the skull

Indeed, during an archaeological FFR project, it is pretty simple to understand that the 3D of the skull represent a 3D documentation, while the 3D of the face is a 3D reconstruction.

I hope this post was useful, Have a nice day!

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