The Vicon Shogun performance-capture system tracks the movements of people and rigid objects that outfitted with retroreflective markers. The Vicon Shogun software is used widely in the creation of movie special effects that involve virtual characters and movie cameras. The markers are 1/4 to 1/2 inch plastic balls coated with the same reflective material used for biking night safety vests. Multiple Vicon cameras are stationed around the performance volume. Each camera has a ring of LED lights that emit invisible infrared light. Each camera sees a dot where light has been reflected from a marker.
When a camera sees a marker, it appears as a two-dimensional circle. To track motion in three-dimensions, the computer must construct a model of the three-dimensional space seen by all cameras. This is done by calibrating the volume by waving a T-shaped wand with several fixed markers. This blue trails of color in the below image represent the how each of the seven cameras saw the wand wave.
wand wave marker trails
As multiple cameras see the wand’s markers from different vantage points, the system is able to solve for the marker’s position in three-dimensions provided at least two cameras see each marker. The Vicon Shogun Live software computes a model of the three-dimensional performance volume including the position and orientation of each camera.
calibrated performance volume
For the first performance-capture tests of the system, we are tracking the position and rotation of rigid body props. Form a rigid body prop by securing about five to eight marker spheres onto a solid object. For example, you might attach markers to a virtual reality headset, a baseball cap, a foam sword, a movie camera, or a tablet device. This image shows how the system sees the eight markers attached to a movie camera.
selected markers that form a rigid body
Because the markers are attached in a fixed configuration on the rigid prop, the computer can solve for the center position of the marker cluster and its orientation axes X, Y, and Z, which appear as the red, green, and blue arrows in the picture below. As the performer moves and turns the rigid body prop, the Vicon Shogun software computes its position and rotation angles in three-dimensional space.
rigid body position and orientation axes X, Y, and Z
The Vicon Shogun Live software streams tracking data to other software applications. For my research, I have written a C++ program that streams the tracking data over a Web socket so that Web programs can access the tracking data.
I selected this system to be the primary tracking system for the new lab because Vicon offers networked license checkout so that people can record motion data in the lab and take it home to replay on their personal computers. Vicon also lets you buy a lifetime license so we don’t need to pay recurring license fees.