The MotionMonitor™ with Optotrak

Principle of Operation

Northern Digital's Optotrak is an active infrared optical position tracking system wherein high resolution sensors detect the 3 dimensional position of a light emitting diode (IRED) through triangulation.  The IRED's are turned on and off in sequence by a strober unit permitting the system control unit (SCU) to identify which IRED is active at any point in time.  As a result, it is not necessary to digitize or manually identify markers nor does the system confuse or interchange markers as they cross one another. Maximum sampling rates  (3500hz Optotrak 3020 and 4600hz Optotrak Certus) and the number of markers determines the maximum frame rate.

Depth of Field

The range in the depth dimension (Z axis) within which the Optotrak system can accurately determine 3 dimensional coordinates is known as its depth of field. The Optotrak depth of field ranges from a minimum distance of 1.5m to a maximum distance of 6m, depending on the focus length of the Position Sensor , a permanent parameter set during manufacture.  Optotrak offers three different focus lengths (close, mid, or far), one of which will best suit your intended application. Please refer to the following guidelines for determining which Position Sensor focus length you need to specify, or contact us directly if you have any questions.

Focus Length

Note that while you can generally measure points beyond the maximum distance recommended below by decreasing the rate at which markers are sampled, you should not measure points closer than the minimum distance recommended. Such close markers may be visible to the Position Sensor (within its field of view), however their infrared signals cannot be properly focused and may produce significant measurement errors.

Close Focus: Close focus is useful when space is limited and the Optotrak Position Sensor must be as close to the markers as possible. For example, you may have a small experiment room, or you may perform surgical procedures that are best studied at close range.

Mid Focus: Mid focus should be used when using the Optotrak at distances beyond 4 meters is not possible or will never be required. Applications such as arm reaching and coordination tasks are well suited to mid focus.

Far Focus: Far focus offers maximum volume of movement. As long as all of your experimentscan be conducted at least 2.2 meters from the Optotrak Position Sensor, far focus is your best choice.

Accuracy & Field of View