Tracking

Gökhan Tekkaya

Gürkan Vural

Can Eroğul

Outline

• Tracking– Overview– Head Tracking– Eye Tracking– Finger/Hand Tracking

• Demos

Tracking - Purpose

• To update the visual display based on the viewers head position and orientation.

• Instead of tracking the viewer's eyes directly, we track the position and orientation of the user's head. From this we determine the position and orientation of the two eyes.

Tracking - Overview

• We may also be tracking the user's hand(s), fingers, legs or other interface devices.

• Want tracking to be as 'invisible' as possible to the user.

• Want the user to be able to move freely with few encumberances

Tracking - Overview

• Want to be able to have multiple 'guests' nearby

• Want to track as many objects as necessary

• Want to have minimal delay between movement of an object and the detection of the objects new position / orientation (< 50 msec total)

• Want tracking to be accurate (1mm and 1 degree)

Tracking Devices - Electromagnetic

• large transmitter and one or more small sensors.

• transmitter emits an electromagnetic field.

• sensors report the strength of that field at their location to a computer

• sensors can be polled specifically by the computer or transmit continuously.

Tracking Devices - Electromagnetic

• uses:– projection based systems, HMDs

• advantages are:– large tracking volume (approx 10 feet / 3 meters) – no line-of-sight restriction – sensors are small and light – technology has been around for a while

• disadvantages are:– affected by metal in the nearby area – latency can be high (0.1 seconds) – accuracy is low in large volumes – somewhat expensive

Tracking Devices - Electromagnetic

• Polhemus:– Motion Tracking:

• LIBERTY LATUS• LIBERTY• PATRIOT• FASTRAK• MINUTEMAN

– Scanning:• FastSCAN

– Eye Tracking:• VisionTrak

Tracking Devices - Electromagnetic

Tracking Devices - Mechanical

• rigid structures with multiple joints• one end is fixed, the other is the object being

tracked• could be tracking users head, or their hand• physically measure the rotation about joints in

the armature to compute position and orientation• structure is counter-weighted - movements are

slow and smooth• Knowing the length of each joint and the rotation

at each joint, location and orientation of the end point is easy to compute.

Tracking Devices - Mechanical

Tracking Devices - Mechanical

• uses:– BOOMs, Phantom

• advantages are:– low latency – high accuracy – sensors are small and light – technology has been around for a while

• disadvantages are:– small volume – only track one object at a time

Tracking Devices - Acoustic

• small transmitter and one medium sized sensor

• each transmitter emits ultrasonic pulses which are received by microphones on the sensor (usually arranged in a triangle)

• as the pulses will reach the different microphones at slightly different times, the position and orientation of the transmitter can be determined

Tracking Devices - Acoustic

• Logitech:– 6 degrees of freedom– 3D and 2D modes– Ultrasonic Technology– High level of ruggedness– PC and Unix compatibility– 250 dpi resolution/ 3D mode– 400 dpi resolution/ 2D mode

Tracking Devices - Acoustic

Tracking Devices - Optical

• LEDs or reflective materials are placed on the object to be tracked

• video cameras at fixed locations capture the scene

• image processing techniques are used to locate the object

• With fast enough processing you can also use computer vision techniques to isolate a head in the image and then use the head to find the position of the eyes

Tracking Devices - Optical

• A. R. T. system from Germany:

Tracking Devices - Inertial

• self-contained

• gyroscopes / accelerometers used

• knowing where the object was and its change in position / orientation the device and 'know' where it now is

• tend to work for limited periods of time then drift.

Tracking Devices - Combinations

• self-contained

• gyroscopes / accelerometers used

• knowing where the object was and its change in position / orientation the device and 'know' where it now is

• tend to work for limited periods of time then drift.

Tracking Devices - Combinations

• Intersense uses a combination on Acoustic and Inertial. Inertial can deal with fast movements and acoustic keeps the inertial from drifting