X hits on this document

PDF document

A Prototype Optical Tracking System Investigation and Development - page 18 / 170

344 views

0 shares

0 downloads

0 comments

18 / 170

4

Introduction and Background

compensate for drift in measurements from accelerometers and gyroscopes.

Electromagnetic trackers, such as the Polhemus Fastrak [9], use magnetic fields to deter-

mine pose. These systems use source and sensor units. DC magnetic fields that are picked up by the sensor unit

The source units create

C or

or units.

Either the source unit

or

sensor

unit

(system

dependent)

contains

three

coils

oriented

so

as

to

create

or

measure

magnetic fields in the three orthogonal directions.

s noted, these systems suffer from

distortions due to ferromagnetic objects in the vicinity of the object being tracked. Unlike optical tracking systems, and to a lesser degree radio frequency tracking systems, magnetic trackers do not require the source and sensor to have a line of sight.

Radio frequency (and microwave) trackers use electromagnetic waves to enable tracking.

Usually these systems use time of flight, however, this is more difficult to implement com- pared with acoustic trackers as the speed of light is many times faster than the speed of sound and precision electronics are required. Perhaps the most well known radio fre- quency tracking system is the Global Positioning System (GPS) run by the United States

Department of Defence [15]. This system uses a constellation of between 24 and 32 Medium Earth Orbit satellites. Using signals from a number of satellites, approximate positional tracking (in comparison to other systems) can be performed. Radio frequency tracking sys-

tems suffer from multipath issues. This occurs when waves bounce off objects and cause multiple signals to be received. This adds to the difficulties of designing a radio frequency tracker. The author is not aware of any precision radio frequency trackers available on the market.

The last type of tracking system and the type chosen for this research is optical tracking. These systems use light sources (optical markers) and optical sensors. The position of the

markers with respect to the sensors enables these systems to calculate pose. some of the available optical systems is given in Section 1.2.

summary of

1.2

Existing optical systems

large amount of work has been performed in the area of optical tracking.

Many op-

tical tracking systems exist and these systems can be broken into two broad categories: inside-looking-out systems and outside-looking-in systems. n inside-looking-out system uses markers outside of the tracking volume. These are observed by the optical system mounted on the object whose pose is being estimated. n outside-looking-in system has the observation component of the system on the outside of the tracking volume and uses optical markers mounted on the object within the tracking volume. n example of an op- tical tracker that uses the inside-looking-out model is the 3rdTech HiBall tracker [16] and

an example of an outside-looking-in tracker is the optical tracking system from

dvanced

Document info
Document views344
Page views344
Page last viewedSun Dec 04 08:40:20 UTC 2016
Pages170
Paragraphs6307
Words54996

Comments