Friday, 21 September 2012

Extreme SfM: fast data acquisition and particular light condition

Hi all,
this post reports some technical informations regarding Cicero's article about Converting pictures into a 3D mesh with PPT, MeshLab and Blender.

The experiment to digitally document in 3D a statue of the Egyptian Museum in Torino (IT) was aimed to hardly test the potentialities of SfM techniques in archaeology. 
The idea just came when I was visiting the exposition with my wife Kathi, during an holiday: I asked the guardians if it was possible to take photos and they answerd me that there were no problems as long as I was not using the flash.
As you can see from the picture below, I found a perfect situation when I reached the first statue's room; the athmosphere was charming, while the sculptures were in darkness, with only a spot light to make them stand out. 

Spot light condition

This particular light condition was a good test for SfM techniques because I could not modify it "artificially" (e.g. with other lamps to get a better illumination of my subject). Moreover I could not use the flash, so I had to turn the ISO of my Nikon D70 to the maximum value, in order to be able to take pictures without the help of a tripod.
Another difficulty arose from the necessity to acquire the data quickly, without disturbing the visit of the other tourists.

The croweded room
Anyway, having increased the ISO of the camera, it was not a problem to collect all the data in just a couple of minutes.

Once home, I tried to do a 3D digital model with SfM and IBM techniques, using Pierre Moulon's PPT. Since I did not think to succeed in my purpose, I did just a fast 3D model, with low quality parameters (scaling all the pictures on a medium resolution). Contrary to what I thougth the model was accurate enought and the experimentation went on thanks to the collaboration of Cicero Moraes, who was able to recreate an high quality texture, using the methodology he described in his post.

The 3D low quality model in Paraview

CREDITS:

This article was possible thanks to the kindness of Dott.ssa Paola Matossi L'Orsa and Dott.ssa Sara Caramello and with the permission from the "Fondazione Museo delle Antichità Egizie di Torino".
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