Motion capture or MoCap is the process of recording an entity, whether it is an object or people, via sensors.
The Motion Capture was performed at the Visgraf Laboratory using OptiTrack, the optical MoCap system of NaturalPoint. It is composed by 12 infrared cameras at 100 fps that keep track of the retroreflective markers which are placed on the dancer's body.
— Markers are to be placed on the body
The system uses the data acquired by the image of the markers to triangulate the 3D position of a subject, using the fact that cameras have overlapping fields of view. There are three main steps. First, the sensors are to be identified on the 2D data recorded by the cameras : we try to keep track of them on each frame. The second step is the 3D reconstruction from the 2D data. We had therefore to calibrate the positions and orientations of the cameras in order to reconstruct the 3D data from at least two different cameras that overlap. Finally, the third step is to apply these data to a virtual skeleton.
Once the markers are placed on the performer's body, it is possible to begin the acquisition, using the Motive software tool that enables us to record movements and export them as BVH files.
In practice, we realized that it is necessary for our use - that is, to record dance movements - to let the performer beat his hands to the music rythm so that we can synchronize the recordings later.
acquisitions
These acquisitions are the result of tests made at the Visgraf Laboratory. Our main problem was the lack of space that reduced the possibilies of danced movements.