Note: Chessboard calibration is the preferred extrinsic calibration method (rather than object calibration).

Extrinsic object calibration trials are used to determine the position and orientation of every camera in your system relative to the desired global coordinate system. Extrinsic object calibration uses the static position of a calibration object with known dimensions or known positions of specific key points on the object. These 3D dimensions or positions must be measured with high precision. The calibration object should be sufficiently large or the calibration key points should be spaced far apart within the capture volume and most points should be visible in every camera view. The key points can be coplanar or can vary in all three global dimensions.

A calibration object file must be created for your calibration object, containing 3D coordinates of the object key points. Each line of the file must contain three comma-separated values representing the global x-, y-, and z-coordinates of the key point, in millimeters. Each key point should be on its own line.

Object calibrations must be performed at the resolution that will be used to record your movement data. If you will be using more than one resolution during your data collection, you must record object calibration trials at each resolution.

Recommendations:

• Record object calibrations trials at a low frame rate (20-30 Hz) to reduce file size and processing time.
• Object calibration trials only need to be a few seconds long.

Recording Object Calibrations:

1. Place your calibration object within the capture volume, at the desired position and orientation to define the global coordinate system.
2. Ensure the key points on your calibration object are visible in every camera view, and there are no obstructions.
3. Begin the recording.
4. After a few seconds, end the recording.

To process extrinsic object calibrations, see Object Calibration.