Tuesday, November 3, 2009

3D scanning and unrolling an ancient seal

A few lines on an interesting recent project I participated and that exploited MeshLab processing abilities.
The project whose results are now shown in a exhibition at the Louvre involved the scanning with non traditional technologies of the very small and wonderful ancient Cylinder Seal of Ibni-Sharrum (photo © CRMF / D. Pitzalis), a precious antique mesopotamic artifact that is considered one of the absolute masterpieces of glyptic art.

This small seal was digitally acquired at CRMF at a very high resolution and with a variety of 3D scanning techniques (microprofilometry, x-ray Tomography, photogrammetric techniques) and, obviously, the results were processed and integrated entirely with MeshLab.

Among the nice things that we did inside MeshLab was the virtual unrolling of the seal, e.g. getting the inverse shape that you get when you roll the seal over a soft substance like clay or wax.  It was quite easy from a technical point of view, but very appreciated by the restorers that disregard invasive plaster based techniques that often can leave small residuals over the precious artifacts.  You can find more details on the whole acquisition and processing of the seal on this VAST conference paper.


On the side you can see a couple of renderings of the 2-million of triangle model of the unrolled seal; the renderings were done inside MeshLab, the first one is a simple flat shaded rendering, while the second one exploit a nice shader that I have recently added to the MeshLab shading arsenal, it mimics in a shameless way the ZBrush technique of varying shininess and color according to the "cavities" of the geometric model (they use it for the famous zbrush wax and bronze materials).  It is nice to see how the shading vastly improve the shape perception of the 3D model.
I have not seen many correct discussion on how to perform these kind of shading, so expects a post on that...

A massive physical reproduction (4 meters long!) of the unrolled seal is at the center of "OnLab" a thematic exhibition of Michel Paysant, that will open in the next days at Louvre, Denis Pitzalis worked a lot on this project and you can find  more details and photos in his blog.


Mark Dow said...

Everything about this is fascinating.

It took me a while to find where the actual size of the object was listed (3.9 cm tall, on the Louvre site sidebar). The conference paper has dimensions on some detail, but not the whole object. A scalebar on the fantastic renderings would highlight the workmanship and reconstruction quality.

Tom said...

This is really interesting and quite timely. It looks like you have had great results.

I am trying (unsuccessfully so far) to unroll a laser scan of a tree trunk covered in WWI and WWII graffiti.

Is the Meshlab module available?

Tom said...

Actually - I can see that it's in there already:
Filters > Smoothing, Fairing and Deformation > Geometric Cylindrical Unwrapping

Thanks very much for this - very useful indeed.

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David said...

I've recently read that 3D laser scanning services are important in archaeology because it enables artifacts to be reproduced as replicas for further studies, among others. It's pretty amazing to think how 3D scanning has developed over the years.

I use the Faro Arm (for sale in some cities) to inspect and measure our assembly parts. With laser scanning, we were also able to produce parts and replicas for prototyping.

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