Thursday, 1 November 2012

Kinect 3D limits: documentation of small objects

As Moreno Tiziani wrote in his post, last Monday (October 22) I was in Padua to start the "Taung Project". The first step of this research was indeed the 3D documentation of the cast of the Taung Child, preserved in the Museum of Anthropology of Padua University
To digitally register our subject we chose SfM/IBM techniques (using ArcheOS and PPT), because, as I reported in this post, the methodology is accurate enough to document small objects. Nevertheless I brought in Padua also our hacked Kinect, to show Moreno how this system is working in 3D recording operations. 

Red circle: Kinect. Green circle Taung Child's cast. Blue circle: RGBDemo compiling on ArcheOS

 As we thought, the cast was too small to be documented with Kinect. The reason is clear: when Kinect is too close, it simply does not "see" the subject to record, while when the device is too far away, it register too few 3D points, so that the final mesh is not accurate enough. 
Unfortunately, I did not capture a screenshot of our test, but I think the images below illustrate the concept: in the first picture my hand is to close to the sensor and it appears completely black, while in the second picture Kinect can see my hand, which appears pink, but the resolution is too low.

The sensor is too close to the subject

The distance between the sensor and the subject is adequate, but the resolution is too low

However we used Kinect to document something in the Museum of Anthropology: a wooden Egyptian sarcophagus. 
As you can see in the short movie below, we registered just one side of the object, for the same reason I explained before: when Kinect is too close to the subject it does not work properly. In this case the position of the sarcophagus was too close to the wall (almost 50 cm) and to a glass showcase (almost 20 cm). It would have been possible to scan all the three visible faces and join them together in post-processing with MeshLab, but this was just an experiment, so we concentrate on the Taung cast. 

However in the movie it is also possible to observe another interesting characteristic of Kinect: being an infrared based device it is not able to go through glass, which is registered like a normal opaque object.

I hope it was useful, have a nice day!


  1. If kinect use a IR laser sensor, the beam will probably suffer reflection or refraction after hit the glass, ergo providing null or wrong measuring values. But if you discard the small object and glass limitation the test is still a success. I think you proved that kinect is a fantastic record tool, not just for archaeologists, but also for art historians or conservators. rgaidao

  2. Hi Ricardo,
    yes Kinect is really an interesting tool. The fact that IR does not go through glass has two interesting consequences (IMHO):

    1) It would be maybe possible to document glass objects, but I never found nothing with adequate dimension to be digitally recorded with Kinect

    2) It is not possible to document directly the whole object shape, positioning it on a glass plate (to register its lower face)

    I tried to register the 3D of some stones putting them on a glass plate (it was important to analyze their shape). I did this experiment with Mattia Segata (Arc-Team's geo-archaeologist), who explained me why Kinect did not work in this case (I did not know that an IR could not cross the glass). We never stop to learn new things... :)


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