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FreeTrack uses a camera to collect real-time information on the point model worn by the user. Specifically the image coordinates of the model points, which are either received directly from the camera or extracted from a video stream. These coordinates are used to generate an estimate of the real head pose, which can be transformed by the user in a number of ways to create a virtual pose. One of the most fundamental transformations involves amplifying rotation so that only small head movements are required. Finally, the virtual pose is sent to the user's choice of outputs. This is all done in the background, with tracking status displayed in the system tray.
A 3D preview is available that shows the virtual head position and orientation for a given real head pose and can be viewed from multiple perspectives, including first-person. This greatly assists with testing and makes it easier to experiment with different settings.
Each degree of freedom (axis) has a response curve that can be modified to change the way the virtual head moves for a given real head movement. This is commonly used to create a central deadzone region so that the user head can be more relaxed there.
Keyboard, mouse and joystick buttons can be used to toggle tracking settings, including the virtual centre location (like adjusting the seat position in a car) and individually toggle axes and outputs.
For NaturalPoint cameras, FreeTrack can provide advanced features and a level of customization that is not available with official software.
Camera
Comparison of some cameras compatible with FreeTrack
Camera
Sensor Resolution
Sub-Pixel Reporting Resolution
Sensor
FPS
Angle()
CPU usage
Approx. price (USD)
In-device Pre-processing
Cheap webcam
320x240
color
30
42
moderate
$20
no
Ideal webcam
640x480
monochrome
60+
42
small
?
no
Sony PlayStation EyeToy
640x480
color
30
56
?
$30
no
Sony PlayStation 3 Eye
320x240 or 640x480
color
120 or 60
56 or 75
?
$40
no
Microsoft Xbox Live Vision
640x480
color
30
?
?
$40
no
Nintendo Wii Remote
128x96
1024x768
monochrome
100
41
none
$40
yes
NaturalPoint TrackIR 1
60k pixels (eg 300x200)
monochrome
60
33
small
retired
yes
NaturalPoint TrackIR 2
60k pixels (eg 300x200)
monochrome
100
33
small
retired
yes
NaturalPoint TrackIR 3
355x288
monochrome
80
33
small
retired
yes
NaturalPoint TrackIR 3 Pro
355x288
monochrome
120
33
small
retired
yes
NaturalPoint TrackIR 4 Pro
355x288 (subsampled at 710x288)
7100 x 5760
monochrome
120
46
small
$99.95
yes
NaturalPoint TrackIR 5
640 x480
96000 x 72000
monochrome
120
51.7
?
$149.95
yes
NaturalPoint SmartNav 1/2
60k pixels (eg 300x200)
monochrome
60
33
small
retired
yes
NaturalPoint SmartNav 3
355x288
monochrome
120
33
small
retired
yes
NaturalPoint SmartNav 4
640x480 (subsampled at 1280x480)
monochrome
100
41
small
$400 to $500
yes
Resolution
In most cases a resolution of 320x240 is sufficient, this is capable of producing a much higher sub-pixel resolution, enough to allow accurate cursor control on a high resolution monitor. Resolutions 640x480 and above have diminishing returns and correspond with an exponential increase in CPU usage when not pre-processed before reaching the computer. Higher resolutions become more important at greater distances from the camera.
Sensor
For the same resolution, monochrome sensors can resolve finer detail much better than color sensors due to the lack of a color filter array.
Frame rate
FreeTrack uses interpolation with low frame rate video devices to improve panning smoothness. However, responsiveness is fundamentally limited to the frame rate; a 30frame/s webcam has a maximum response delay of 33.3 milliseconds compared with 8.33 milliseconds for a 120frame/s camera. To put this into perspective, a human reaction time to visual stimulus (finger reflex) is typically around 200ms, 30ms can be regarded as a competitive ping in online reflex-based games and an LCD monitor refresh rate is typically 17ms.
Higher responsiveness gives a greater feeling of control but since virtual head motion is amplified it can also cause it to move unrealistically fast. For this reason, some programs limit head movement speed, wasting some of the responsiveness of higher frame-rate cameras.
Angle
A wider viewing angle allows a larger tracking region when in close proximity to the camera. At further distances a wide angle is not desirable, more of the frame is unused and the effective resolution drops more rapidly. More peripheral light can also be seen which can interfere with tracking. Viewing angle can be reduced by using digital zoom at the cost of resolution.
CPU usage
The Nintendo Wii Remote effectively uses no CPU, NaturalPoint cameras use a small amount and general video devices can use a significant amount depending on the brand and the specific camera settings in use. A Playstation Eye running at the same resolution and frame rate as a TrackIR 4 would be very demanding on a single-core CPU. However, modern multi-core CPUs are making this less of an issue. Resolution and frame rate can always be reduced to conserve CPU resources.
Filters
For reasons of efficiency, FreeTrack requires the tracking points to be isolated from all other light, this is best done using infrared LEDs and a visible-light blocking filter in front of the camera. Photographic film or the magnetic storage medium inside floppy disks can be used as inexpensive visible-light filters. Further filtering can be done in software by adjusting exposure and threshold.
All video devices like webcams have a built-in infrared blocking filter which can be removed to improve sensitivity to infrared light, allowing better point isolation and the possibility of retroreflective tracking. This is normally a straight-forward and reversible procedure for most webcams.
Wii Remotes and NaturalPoint cameras are designed for infrared point tracking so already have visible-light blocking filters.
Point model
Model configurations
Single point: a single tracking point, for example attached on a baseball cap or wire that extends forward of the head. Can be easily achieved with a small light source like a penlight. Unlike other configurations, this is limited to two degrees of freedom (yaw and pitch) and can be more sensitive to translation than rotation.
Three point clip: asymmetrical triangular arrangement of points that can be clipped to headphones and positioned to the side of the head.
Three point cap: symmetrical triangular arrangement of points, typically attached to the rim of a baseball cap.
Four point cap: symmetrical non-coplanar arrangement of points, also attached to the rim of a baseball cap.
Models can be made in a DIY fashion at minimal expense using readily available electronic components. Component kits and fully constructed models are also available for purchase from some members of the FreeTrack community.
Active points
An active point model uses visible or infrared LEDs (5mm or larger) to represent the tracking points, powered by battery, transformer (plug pack) or USB. The electric circuit is very basic and can be made by someone with little or no experience with electronics.
Common LEDs, like those found in remote controls, have a narrow, highly focused beam which is not suitable for optical motion tracking. They can be easily turned into wide angle LEDs by filing their lens tips down flat. Alternatively, wide angle LEDs can be purchased from specialist electronics retailers, like the infrared Siemens/Osram SFH485P, with a half-angle of 40 degrees.
Reflective points
Retroreflective material can be used to represent the tracking points by illumination with an infrared light source. This configuration doesn require wires or batteries connected to the user but is more susceptible to interference by background light. In most cases a webcam internal infrared blocking filter needs to be removed to increase sensitivity enough that the infrared light reflected by the tracking points can be seen.
FreeTrack interface
FreeTrack has a simple interface that can be freely used by third party programs to access 6DOF tracking data, both real raw measurements and virtual. It is hardware agnostic, so is not dependent on a specific brand or version of hardware and can be used without restriction. Bohemia Interactive's ARMA 2 is the first game to support the FreeTrack interface.
TrackIR interface
This section may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (February 2010)
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Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (February 2010)
The TrackIR interface SDK is only available from NaturalPoint Inc. under a signed license agreement and is covered by a NDA, so while FreeTrack is open source, the TrackIR interface component is required to be closed source.
NaturalPoint believe that the use of FreeTrack to gain view control in TrackIR Enhanced software is a violation of their copyright.[citation needed]
Most TrackIR Enhanced software need to be provided with text strings which bear notice of "EyeControl Technologies" copyright (former name of NaturalPoint, Inc.) in order to activate the TrackIR Enhanced interface.[original research?] Software which requires these text strings for interface activation also contain the strings themselves.[original research?] At NaturalPoint's request, FreeTrack project members removed the strings from the software they provide to end users.[citation needed] FreeTrack then implemented a workaround which creates a local copy of these strings from the client software when used with TrackIR Enhanced titles.[citation needed][original research?] FreeTrack project members argue that copyright is not violated in this case since it may fall under the provision of 17 U.S.C.117.[citation needed] The text strings are a necessary and functional part of the interface which FreeTrack project members believe makes them exempt from copyright for the purposes of interoperability.[citation needed]
In late 2008, NaturalPoint started using an encrypted data stream in version 4.1.036 of their TrackIR software, making it more difficult for third party software like FreeTrack to interface with TrackIR enabled software titles. The first title that required the new data stream was DCS: Black Shark. The FreeTrack community responded by making a utility called TrackIRFixer which disables the decryptor in the game client so that unencrypted data can be accepted. Because the fixer modifies files, it is incompatible with some forms of DRM and online anti-cheat. Two years after encryption was introduced, there are still some TrackIR enabled games being released that are not using encryption.
TIRViews is a dynamic-link library distributed as part of the TrackIR software, it provides special support for a small number of mostly older games by using game interfaces or memory hacks to facilitate view control. Though a violation of the TrackIR software's EULA, it is possible to use TIRViews with FreeTrack.
See also
Free software portal
List of games supporting FreeTrack
TrackIR
References
^ DeMenthon, Daniel; Larry S. Davis (1992). "Model-Based Object Pose in 25 Lines of Code". European Conference on Computer Vision: 335343. http://citeseer.ist.psu.edu/rd/67111319%2C110936%2C1%2C0.25%2CDownload/http://citeseer.ist.psu.edu/cache/papers/cs/5521/http:zSzzSzwww.cfar.umd.eduzSz~danielzSzdaniel_papersfordownloadzSzPose25Lines.pdf/dementhon95modelbased.pdf.
^ Alter, T. D. (1992). "3D Pose from Three Corresponding Points Under Weak-Perspective Projection". pp. 43. http://citeseer.ist.psu.edu/rd/29809521%2C524747%2C1%2C0.25%2CDownload/http://citeseer.ist.psu.edu/cache/papers/cs/26154/ftp:zSzzSzpublications.ai.mit.eduzSzai-publicationszSzpdfzSzAIM-1378.pdf/alter92pose.pdf.
^ a b "TrackIR3 Pro heads-up game controller". ars technica. http://arstechnica.com/reviews/hardware/trackir3pro.ars/2. Retrieved 2007-10-13.
^ a b c d "TrackIR Product Comparison". NaturalPoint. http://www.naturalpoint.com/trackir/02-products/trackir-product-comparison.html. Retrieved 2007-10-13.
^ a b "SmartNav Older Model Comparison". NaturalPoint. http://www.naturalpoint.com/smartnav/products/older-model-comparison.html. Retrieved 2008-11-01.
^ "File: ARMA 2 Update 1.05". http://www.arma2.com/support/updates/file/219-arma2update_105.html?lang=en. Retrieved 2010-02-20.
^ "TrackIR Developers: Which SDK Do I Need?". http://www.naturalpoint.com/trackir/05-developers/which-sdk.html. Retrieved 2010-02-20.
Daniel DeMenthon's academic page - papers and examples of POSIT algorithm
FreeTrack YouTube channel
Categories: Game controllers | Video game hardware | Virtual reality | Windows-only free software | Computer accessibilityHidden categories: Articles that may contain original research from February 2010 | All articles that may contain original research | Articles needing additional references from February 2010 | All articles needing additional references | All articles with unsourced statements | Articles with unsourced statements from February 2010
