Sunday, 24 March 2013

Extreme SfM: underwater archaeology

Hi all,
It is long that Alessandro and me wanted to write this post, but for one reason or another, we could not work on it. 
Today I decided to do it in order to answer two questions that people often asked us during conference or lessons:

1) Is it possible to work with SfM/IBM techniques underwater?

2) Is it possible to extract 3D from a movie?

As regards the first question, I can report that since we (Arc-Team) started to work with SfM and IBM (2009), we did also tests underwater and they gave us positive results. This is one of the main reason why we invested so much time on the research in this filed: SfM and IBM methodology, until now, is one of the best solution in archeology, due to its versatility (it can be used for underwater or aerial documentation, in low light conditions or in precarious situation, during mission abroad, etc...). We already underlined this concept when, with the help of Nicolò Dell'unto (Lund University), we compared different methodology to record 3D documentation of archaeological artifacts. The result of this experiment was presented during the ArcheoFOSS 2012, in Napoli (see the related slides and this post). During the workshop "Low cost 3D: sensori, algoritmi e applicazioni", we had the opportunity to better analyze the use of SfM/IBM in extreme working conditions, strengthening our point of view about this methodology (see the related slides). 
The image below is an example of an aerial 3D documentation done with an open source UAV and Python Photogrammetry ToolboX...

Aerial documentation with a KKopter and ArcheOS (PPT)
... while this other image shows the results we achieved using some pictures that Victor Jansa, of TUWA ("Tauchverein für Unterwasserarchäologie"), sent us to do a test.

Test with Victor Jansa's pictures (done with PPT)

In order to answer the second question, I can say that, facing our experience, it is possible to reconstruct 3D models from videos (and I guess this is one of the aims of SfM itself). We did some tests about this topic, getting acceptable result (at least regarding our primary target, which was to have a fast 3D object for further modeling operations). As an example, I can report one of the last post of Cicero Moraes, who used SfM from a youtube clip to get a 3D skull for forensic facial reconstruction aims. The image below is taken from Cicero's photo album:

3D skull obtained with SfM techniques from a movie

For a better explanation of what I wrote above, I think it is worth to show the results of a project we are undertaking since 2005 (trying to support Prof. Tiziano Camagna on his exploration of Tovel's Lake, in Trentino).  During this project we did several surveys, diving in different parts of the lake and especially in the South-West area, where lies a forest which is now underwater. In 2012 Tiziano Camagna and Andrea Forti, despite the low visibility, where able to record a short movie of some of the threes. We used this video for a fast 3D reconstruction, because it was particularly indicated, due to its characteristics: it was recorded for no SfM aims (as you see the movie sequences are not optimal for a 3D reconstruction), it represents the normal turbidity condition of the lake and it was done with an high lens distortion camera (GoPro Hero 2). For such reasons this material was perfect to hardly test SfM and IBM techniques for underwater archeology. In this animation you can see a short part of the movie (from the 15th second  to the 25th), which we used for the 3D documentation...

From "La foresta sommersa del Lago di Tovel" (T. Camagna, A. Forti)

... and here you can see the result:

I hope this post was useful. Soon, when the season will allow us to start diving again, we will go on with tests and experiment related with underwater archeology. I hope to write soon some new report about it.

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