Home » Basics » Optical Tracking

Basic Principles of Optical Tracking

What is optical tracking?

The goal of optical measurement technologies is to calculate the exact pose (position and orientation) of a tool, object or person within a pre-defined coordinate system. Optical motion-trackers typically use multiple two-dimensional imaging sensors (cameras) to detect "active" infrared-emitting or "passive" retro-reflective markers affixed to some interaction device. Based on the information received from multiple cameras, the system is able to calculate the location of every marker through geometric triangulation. When more than two markers are grouped together to form a rigid-body target, it becomes possible to determine the target's orientation, yielding a total of six degrees of freedom (6-DOF).

How does it work?

Step 1: The iotracker system uses passive rigid-body targets composed of retro-reflective spherical markers. The markers' special coating reflects most of the infrared light emitted by an iotracker camera's built-in LED-strobe back to the imaging sensor.

optical tracking basics - infrared strobe and reflection

Step 2: The iotracker software runs advanced image processing algorithms to calculate the projected centers of every marker in every camera image.

optical tracking basics - image segmentation, self-occlusion

Step 3: The 3D location of every marker is recovered via geometric triangulation.

optical tracking basics - triangulation

Step 4: The iotracker software identifies pre-calibrated rigid-body targets and computes their position and orientation (6-DOF pose).

optical tracking basics - pose estimation