Flock of Birds info

[Nancy Hamilton]

Dear Biomch-L'ers
I recently posted a query about a "flock of birds" set-up that I saw on
T.V. Much to my surprise it is not a particulary new technology and a number of
peolpe had very thorough information about such systems. I have compiled the
responses I received for all to share (including one blatant commercial which
does contain a lot of valuable technical info). While it seems that some are redundant,
I have included all in order to also give information on current users and what
their experiences have been. My thanks to all of you who responded. To those of
you who asked for any information I found, I hope this helps.


Thanks again -

Nancy Hamilton

One and only biomechanist
University of Northern Iowa
Cedar Falls, IA

hamilton@uni



From: IN%"vmcdonald@plato.jsc.nasa.GOV" 31-AUG-1994 13:18:10.77
To: IN%"Nancy.Hamilton@cobra.uni.edu"
CC:
Subj: RE: Saw a new system



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>I happened to be watching Dateline NBC last night and saw a motion recording
>system that blew me away. The system consisted of sensors taped to various
>points on a dancers body (looked like duct tape - no mention of what type of
>sensors), then attached to an overhead cable system which was connected to a
>large bank of input devices of some type called a "flock of birds".

Nancy,
I'd be happy to talk to you about this system if you are
interested. You can reach me at 713-212-1489. For your information I have
included a file (from the manufacturer) which describes the system in more
detail.

I am not affiliated with Ascension in any way. I just happen to be a user
of their system

--Vernon



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Thank you for your interest in our product, Flock of Birds 6D tracker.
Some of the benefits of our product are:

* Full 360 degree coverage without blocking or echoing problems,
* Fast measurement rate -- up to 144 position and orientation
measurements per second,
* Lowest lag of all trackers when tracking multiple points,
* Simultaneous tracking of up to 30 separate independent points
(targets) without degradation in update rate or dynamic performance,
* Proven long-range performance, out to =D2 8 feet,
* Free interface software with source code,
* Compatible performance and integration with most VR hardware and
software systems,
* Lowest priced 6D magnetic tracker in the marketplace.


We would like to send you our standard information package. Please
provide us with your mailing address.

Included with this message is some general information about our 6D
tracker. Please contact us if you have any questions.

Regards,
Jack Scully
Ascension Technology Corporation



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A Flock of Birds(TM)
6D Multi-Receiver/Transmitter Tracking Device

A Flock of Birds delivers what no other six degrees-of-freedom
measurement device can-simultaneous tracking of up to 30 tiny receivers.

Each receiver makes up to 144 position and orientation measurements
a second. Each transmitter allows operation about a three foot radius. Range
may be increased up to =D28 feet with the Extended Range Transmitter option.
Linked together, the Flock's transmitters provide enough coverage for a
virtual world to literally fill a room.

To minimize the delay between spatial measurements and presentation
of visual scenes, the Flock uses multiprocessors to reduce computation time
and a Fast Bird Bus (FBB) to speed data transmissions to the user's host
computer. The result is real time availability of sensed motions for graphics
and measurement applications ranging from simulation and virtual reality to
biomechanics and entertainment.

A Flock of Birds is designed for flexibility and responsiveness to
multiple needs. In the One Transmitter-Multiple Receiversmode, up to 30
receivers operate in the user's space surrounding a single transmitter. These
receivers may be attached to one's head, hands, arms or legs, In the Walking
Bird mode, many transmitters are geometrically fixed in a large area. Their
signals are activated and deactivated as one walks about them. Whether one
straps on one or 30 receivers, the Flock updates each receiver up to 144 times
a second.

By fostering new and exciting interactions with computer graphics, A
Flock of Birds further enriches our pursuit of communicating with computers in
human terms.

Ascension
Technology Corporation



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Technical

Translation range: plus or minus 3'(8' optional) in any direction
Angular range: plus of minuw 180 degrees Azimuth & Roll
plus or minus 90 degrees Elevation
Translation accuracy: 0.1" RMS
Translation resolution: 0.03"
Angular accuracy 0.5 degrees RMS
Angular resolution 0.1 degrees RMS @ 12"
Update rate: Up to 144 measurements/second
Outputs: X,Y,Z positional coordinates and orientation
angles or rotation matrix
Interface: RS-232C with selectable baud rates to 115,200;or
RS-422/485 with selectable baud rates to 310,000
Format: Binary
Modes: Point or stream


Physical

Transmitter: 3.75-inch cube (internally mounted in Enclosure or
externally mounted with 10' cable) or extended range
transmitter option: 12-inch cube externally mounte with
20' cable

Receiver: 1.0" x 1.0" x 0.8" cube (or optional 3-button mouse)
with 10' or 25' cable

Enclosure: 9.5" x 11.5" x 2.6"

Power: User provided or optional external plug-in: US/European
version

Environment: Large metallic objects in operating volume may degrade
performance


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COMMENTS FROM THE FIELD


PERFORMANCE OF THE FLOCK OF BIRDS


Here's a sampling of what people are saying about their Flock trackers:


The long-range Flock is a brilliant tool for absolute real time, full-
body tracking. More important than the hardware though is the
responsiveness of the Ascension team in working with us to integrate all
the pieces into a working animation system.

Chris Walker, President
Mr. FILM


The Ascension Bird is very reliable. It performs faultlessly even after
18-hour days in Virtuality (SD), our VR leisure simulator.

Richard Holmes, Design Director
Virtuality Entertainment, Ltd.


The Flock with an ERT (Extended Range Transmitter) is the only tracker
I've used that becomes part of the solution instead of part of the
problem. It does the job well enough to become a transparent element of
a VR system, allowing me to focus on other issues. It has enough range
to allow reasonable movement in many applications without the user having
to be conscious of the tracking area. I have used it in unpredictable
and demanding environments, such as on stage for musical performances,
and it has always proven to be reliable. It also shows markedly less
susceptibility to signal degradation in the presence of other devices
such as displays, when compared to other non-line-of-sight trackers.

Jaron Lanier, VR Developer & Musician
Founder of VPL Research


I have the highest regard for the people at Ascension Technology and
their products. Since our purchase of the Flock of Birds, we have had
nothing but prompt and expert answers to our questions. From phone
support to on-site visits, Ascension engineers have always shown the
utmost enthusiam toward making our installation the best possible.
Because of the durability of the hardware, we expect to rely on our Flock
for years to come.

Jeff Thingvold, Senior Software Developer
Lamb & Co.


With a combination of state of the art Silicon Graphics Reality Engine
graphics, motion sensing equipment from Ascension (seven receivers with
long range tracking) and our proprietary software, we've broken into a
brand new art form. We've gone from Waldo puppetry to the fully
articulated computer-generated figure.

Graham Walters, Senior Animator
Pacific Data Images



COMMENTS FROM THE FIELD (Continued)

PERFORMANCE OF THE FLOCK OF BIRDS


The Flock of Birds with long range tracking gives us the high speed
position and orientation outputs we need to drive a fully articulated
human figure. It adds a whole new dimension to JackTM, our comprehensive
human modeling software program.

Norman Badler, Chairman
Dept. of Computer and Information Sciences
University of Pennsylvania


The Flock of Birds with its Extended Range Transmitter gives us the range
we need for group VR. It lets us accommodate 10 people in a 1000 cubic
foot space. In the Cave, it meets all our expectations for head and hand
tracking in real time.

Tom DeFanti, Co-director
Electronic Visualization Lab
Univ. of Illinois @ Chicago


The Flock works extremely well with our VR development software running
on a PC. We have integrated it with a helmet-mounted display to let users
move through 3D environments in real time.

Ed LaHood, President
VREAM, Inc.


I found the Flock to be an excellent tracker. Easily the best system I
have experienced in terms of pure tracking. Lag time is acceptable and
the smoothness of the data is impressive.. From 4 feet to the end of the
range - 9 feet - the tracker data remains stable and the outputs of the
two receivers I tested appear correct relative to each other. The system
is flexible and easily extensible. I also found it simple to write good
diagnostics due to the information available on the system. [Evaluation
results: testing of Extended Range Flock with two receivers.]

Andrew Dickerson, Production Manager
Division Ltd.


When we first approached the major tracker manufactures about making
their trackers optional with our HMD, Ascension was the only firm that
gave us 110% effort to get the job done. The fact that we sell more
Ascension Birds with our products than any other tracker is a testament
to their quality.

Shannon O'Brien, Director, Marketing & Sales
Liquid Image Corp.





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AVAILABLE FOR
FLOCK OF BIRDS TRACKERS



Company -----
Product ------
Platform -------
Application ---------
Contact Phone

Alias
PowerAnimator 5.0
SGI
Character Animation
Gary Mundell 416-362-9181

Softimage
Channels 2.6
SGI
Character Animation
David Morin 514-845-1636

Wavefront
Kinemation
SGI
Character Animation
H.B. Siegal 805-962-8117

UPennGraphicsLab
Jack Human Factors Analysis Software
SGI
Human Factors Modeling
John Geldening 215-898-9585
Mike Hollick 215-898-0587

VisualCircuits
3D Studio Driver
PC
Bird Interface
Dan Sullivan 612-560-6205

RPI
CDK Driver
PC
Interface to Autodesk's Cyberspace Developer's Kit
Scott Redmond 415-495-5671


HIT
Lab Mercury
SGI/PC
Interface w/ VR Databases
Andy MacDonald 206-685-8625

Straylight
Photo VR
PC
Interaction w/ VR Worlds
Tony Asch 908-580-0086

VREAM
VR Development System
PC
VR Development System
Ed LaHood 312-477-0452

Dimension Internataional
Superscape VRT3
PC
VR World Creation
Ian Andrew 44-734-810-077

SimGraphics
VR Workbench
SGI
Real Time 3D/VR Interaction
Dave Verso 213-331-9148

Sense8
World ToolKit
=20 SGI/PC
VR Simulation
Tom Coull 415-331-9148

Computer Explorations, Inc.
CyberView
PC
Cyberspace Creation View & Interaction
Earendil Spindelilus 205-882-9490

Cyberzone
CDK Driver
PC
Interface to Autodesk's Cyberspace Developer's Kit
Eric Landry 813-359-8394



Gravity Int.
Virtual Enviroments
SGI
VR Worlds Development
Dale McGrew 415-579-1125



Swedish Institute of Computer Graphics
DIVE
PC
3D Navigation in in VR Space
Christer Carlsson 46-8-752-1560


As of 11/12/93



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COMPARISON WITH POLHEMUS TRACKERS

Q. Is the Ascension Flock the same as a Polhemus tracker?

No, the two companies have developed and patented differing magnetic
technologies. Ascension trackers employ a pulsed DC technology; Polhemus
trackers employ an AC electromagnetic technology.

>From a user's viewpoint, Ascension trackers offer three advantages over
Polhemus trackers: simultaneous tracking of multiple receivers, reduced
distortion in the presence of metals, and proven long range performance.

These advantages will be discussed in detail in our responses to the
specific questions below.

Q. What do you mean by simultaneous tracking of receivers?

The Flock processes its outputs in parallel to minimize the delay
between motion capture and the output of a data record. It does this by
dedicating one microprocessor along with associated electronics to each
receiver in the Flock. By so doing, the so-called multiplexing problem,
which halves the output rate of Polhemus AC electromagnetic trackers, is
eliminated. For example, while the Polhemus AC tracker makes 120
measurements/seconds for a single sensor, the rate drops to 60
measurements/seconds for two sensors and to 30 measurements/seconds for
four sensors. Whether tracking one or 30 receivers, the Flock maintains
its high update rate of 100-144 measurements/ receiver/second. This feature is
especially important in maintaining fast dynamic performance is simulator
and virtual reality applications in which the most important tracker
consideration is data latency or lag. Multiprocessing enables the Flock
to offer the fastest dynamic performance available whenever more than one
receiver is tracked.

Q. What do you mean by independently tracking each receiver?

Each Bird receiver is individually tracked. Regardless of the number of
receivers in a Flock, each reports its unique location in space without
interfering with one another. Each Bird receiver is also assigned its
own unique address, via dip switch settings, so the host can identify,
send, and receive commands from any one Bird receiver along a dedicated
communications bus, called the Fast Bird Bus (FBB).

Q. Why use DC magnetic fields?

The DC magnetic approach overcomes the two primary limitations of other
tracking technologies: (1.) the need to maintain a clear line of sight
between a transmitter and receiver and (2.) the distorting effects of
nearby metals.

The Flock's transmitter emits a series of DC fields that are not
obstructed or occluded when their path to a receiver is blocked by a
head, hand or other object. Devices using light or sound energy, on the
other hand, must maintain a clear path or data will be lost until it is
restored.

Of equal importance is the fact that pulsed DC field do not continuously
generate eddy currents in nearby metals. It is this eddy current problem
that badly distort measurements in magnetic devices, such as the Polhemus
which uses AC electromagnetic fields. The problem with AC trackers
becomes noticeable when they operate in close proximity to conductive
metals, such as stainless steel and aluminum. Because of their rapidly
varying nature, AC fields continuously induce eddy currents in nearby
metals, causing significant distortions in measurements. Ascension
trackers, on the other hand, take advantage of the inherent
characteristics of steady (DC) magnetic fields, which do not cause
continuous eddy-current effects. As a result, Flock trackers are
generally 3 - 10 times less susceptible to conductive-metal interference
than AC systems. For this reason they are commonly used in many
environments precluding the accurate use of AC trackers.

Ascension's DC signal format is also less susceptible to errors when
used in the presence of ferrous metals, such as iron and carbon steel.
Of particular concern is the steel rebars in many floors. While both the
DC and AC systems are increasingly affected as transmitter to receiver
separation increases, the DC approach typically experiences errors in
position and orientation that are five times smaller than the AC system
errors.

Q. How does the long range performance of the Flock and the Fastrak compare?

The Flock is the only magnetic tracker offering an optional long range
transmitter (ERT) designed for graphics applications. The ERT's signal is
sufficiently strong to allow the accurate measurement of the position and
orientation of multiple receivers as far as 8-feet away. This radial
separation permits one to walk around a 12-foot by 12-foot room.
Operation beyond this separation is possible with reduced accuracy.

For ultra-long range performance, additional ERTs may be arrayed
together. An array of four ERTs, for example, lets one walk around a
24-foot by 24-foot room.

The Polhemus Fastrak provides "specified accuracy when the receivers are
located within 2.5 feet of the transmitter. Operation with separations up
to 10 feet is possible with reduced accuracy." (Source: Fastrak
Operations Manual.) While this technical information clearly states
range limitations, Polhemus advertisements, on the other hand,
consistently sell operational performance at the 10-feet range. Potential
purchasers should take note that Fastrak users report that due to noise
constraints, Fastrak outputs are rarely useable beyond a range of 4.5 feet.

Because of its proven long-range performance, among other things, Flock
trackers are the unanimous choice of animation studios and developers
using magnetic tracking systems for motion-capture. The three major
animation software providers, Alias, Softimage, and Wavefront currently
recommend the Flock as the "preferred" method for capturing human
motions in character-animation applications.

Q. Do I need to set up multiple Flock transmitters, like is done with
the Fastrak, when I operate multiple receivers?

No. One Flock transmitter's magnetic field can be measured
simultaneously by all receivers in use -- regardless of their proximity
to one another. We are able to do this because each Bird receiver in the
Flock operates with its own independent computer linked to one another
by a dedicated communications bus (also known as the FBB).

The Polhemus Fastrak is capable of tracking four receivers (sensors)
with a single transmitter. But, as mentioned, at a greatly reduced
update rate. Each subsequent set of four sensors requires the add ition
of another transmitter operating at a discrete carrier frequency. To do
this, multiple Fastrak transmitters must be aligned and calibrated in the
user's working area. If this is not precisely done or if a transmitter's
location is bumped then its tracker outputs will exhibit jumps as one
moves about a work space.




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KEY PERFORMANCE PARAMETERS OF ASCENSION & POLHEMUS TRACKING DEVICES


Parameter Ascension Polhemus Polhemus
Flock of Birds Isotrak II Fastrak

Measurement Rate
(Measurements/sec)
1 Receiver 144 60 120
2 Receivers 144 30 60
@ Max Number of Rcvrs 144 30 30

Maximum Number of Receivers 30 2 32

Number of Transmitters to 1 1 4
Support Max Number of Receivers

Maximum Data Output Rate 312K 115K 115K
(Baud or Bytes)

Lag Increase with Multiple No Yes Yes
Receivers**

Range - Standard Transmitter 3' 5'* 10'*
- Extended Transmitter 8' N/A N/A

Accuracy Degradation Due to:

Conductive Metals Low High High
Stainless Steel None High High
(300 series)=09

CRT Interference Rejection Yes No Yes

LCD Noise Susceptability No Yes Yes

Unit Cost (1 Receiver) $2,695 $2,875 $5,750


* Note 1: Polhemus specifies range at maximum transmitter-sensor
separation distances. At these ranges, outputs will contain significant
amounts of noise, which may render their measurements worthless. We
will provide you with a number of references who have independently
assessed actual range performance of both Ascension and Polhemus trackers.

** Note 2: For a complete discussion of latency in competitive motion
trackers, contact Ascension.





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6D Multi-Receiver/Transmitter Tracking Device


Part Number Description (Standard Unit) List Price
($)

600201 Model 6DFOB Flock of Birds Electronics Unit 1,675.00
in an Enclosure

600205 Standard Flock Transmitter with 10' Cable 450.00

600001-B Receiver with 10' Cable 450.00


The above unit includes: Sync Pick-up Assembly, Interface Software Diskette
and Installation & Operation Guide.

Note: Each Flock electronics unit controls a maximum of one transmitter and
one receiver. For each additional transmitter and/or receiver, an additional
electronics unit must be added. If an optional power supply is required, add
one for each purchased electronics unit.



TRANSMITTER OPTIONS

600305 * Extended Range Transmitter (ERT) with 2,395.00
20' Cable (also Requires Controller Unit)

600301 * ERT Controller Unit (for Controlling up 3,450.00
to Two ERTs)

600300 ERT Controller Expansion Unit (for Controlling 545.00
Two Additional ERTs)

FLOCK OF BIRDS OPTIONS

600200 * Model 6DFOB Flock of Birds Electronics 1,575.00
Unit on Circuit Board (without Enclosure)

600002 * Receiver in 3-Button Mouse with 10' Cable 795.00

600304-B * Receiver with 25' Cable 450.00

100059 External Power Supply 120.00

930000 Extended Warranty per Flock Unit (Adds One Extra Year) 495.00

* These options are available in lieu of standard unit part(s)




----- Ascension Technology Corporation ----
Sales ATT: Jack Scully
Technical Support ATT: Steven Work
Voice: (802) 860-6440 FAX: (802) 860-6439
Internet: ascen@world.std.com
Address: PO Box 527, Burlington VT 05402 USA
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__________________________________________________ ______________
Vernon McDonald Motor Performance Lab.
KRUG Life Sciences NASA/Johnson Space Center

vmcdonald@plato.jsc.nasa.gov
__________________________________________________ ______________



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From: IN%"dooley@eng.clemson.EDU" 31-AUG-1994 13:50:52.70
To: IN%"Nancy.Hamilton@cobra.uni.edu"
CC:
Subj: RE: Saw a new system

The Flock system is a 3 dimensional sensing system manufactured by
Ascension technology Corp., Burlington, Vermont. There phone number is:
802-860-6440.
There internet address is: ascension@world.std.com

I have several of their transmitters and receivers in a virtual reality
system and they work well.

-------
R. Larry Dooley
dooley@eng.clemson.edu


From: IN%"vmcdonald@PLATO.JSC.NASA.GOV" "Vernon McDonald" 31-AUG-1994
14:18:`
To: IN%"BIOMCH-L@nic.SURFnet.nl" "Multiple recipients of list BIOMCH-L"
CC:
Subj: RE: Saw a new system

Nancy.Hamilton writes:

>I happened to be watching Dateline NBC last night and saw a motion recordin=
g
>system that blew me away. The system consisted of sensors taped to various
>points on a dancers body (looked like duct tape - no mention of what type o=
f
>sensors), then attached to an overhead cable system which was connected to =
a
>large bank of input devices of some type called a "flock of birds"

The system you saw is manufactured by Ascension Technology and works using
a DC magnetic field. Each "sensor" attached to the body montiors 6 degrees
of freedom (3 translation and 3 orientation). These systems (a competing
one is manufactured by Polhemus) are used extensively in virtual reality
applications. We are in the process of implementing the use of the "Flock"
for measurement of human segmental motion during a postural control task.
The system is built for sampling via an RS232 port (PC, MAC or Unix
Workstation) and can sample up to max of 144 Hz.

The systems vary in number of sensors, range, number of transmitters, etc.
But a 4 "sensor" system with a range of =B13ft runs about $8500.

The company can be contacted at:

Ascension Technology
PO Box 527
Burlington VT 05402

802-860-6440


--Vernon McDonald


From: IN%"keith@cvs.rochester.EDU" 31-AUG-1994 15:52:44.77
To: IN%"Nancy.Hamilton@cobra.uni.edu"
CC:
Subj: RE: Saw a new system

I use the flock of birds system to study hand movements. It is an electro-
magnetic search coil system. It records up to about 144 Hz (half that with
two sensors, etc). Precision to about +- 1cm in translation and +-2 degrees
in orientation. It is pretty cheap (I think about $5k for base system) comes
with software for dos environment..... Drawbacks are that it is very
sensitive to metal in the environment. Can't have any metal between emitter
and sensor. Also you are tethered by the cables....
Contact Ascension Technology Corp. Burlington, Vt. I don't ahve the phone
or e-mail contact info. Well you might try phoning 802-655-7879. I think the
number may have changed as they moved recently....

Keith Karn
keith@cvs.rochester.edu

P.S. Polhemus makes a similar system.



Hi, Nancy,

I believe it is a "birds" based system. It generates a magnetic field
and then uses sensors each consists of three coils to sense the 3-D
location of the attached object. One of students, M. Sati at Ecole
Polytechnique de Montreal (sati@grbb.polymtl.ca) has been using
"birds". You can contact him for further information.

Regards.

************************************************** ********************
Steve Y. Yang | Internet: yyang@bnr.ca | The above opinions |
P.O. Box 3511, Stn 'C' | Tel: (613) 763-4376 | are mine, not |
Bell-Northern Research | ESN: 393-4376 | those of Bell- |
Ottawa, Ontario | Fax: (613) 763-7241 | Northern Research. |
K1Y 4H7 [CRK 040] | | |
************************************************** ********************



From: IN%"ikirtley@info.curtin.edu.au" 31-AUG-1994 19:13:47.50
To: IN%"Nancy.Hamilton@cobra.uni.edu"
CC:
Subj: RE: Saw a new system

Dear Nancy,

The Flock of Birds, or at least it's predecessors, ISOTRAK and FASTRAK
(which we have here) is nothing new. It's an inductive device developed
from the GPS satellite navigation technology. It is quite nice for real
time recording of movement, but there are problems if you want to do
anything important.

For example, if you want to calculate joint moments (which I personally
think is the main reason, perhaps ONLY reason, for doing motion analysis -
rather than just videoing), you need kinematics measured with respect to
the global reference frame. I am not sure that Flock of Birds can do this.

I'd be grateful if you'd let me know what you discover on this point. The
company who makes it is called Polhemus Inc., PO box 560, Colchester, VT
05446, fax 8 302 2766.

Best of luck!
Chris

__________________________________________________ __________________
Dr. Chris Kirtley MB ChB, PhD c.kirtley@info.curtin.edu.au
^
Lecturer, Bio-engineering --_ / \
/ \
School of Physiotherapy, Perth #_.---._/
Curtin University of Technology, V
GPO Box U1987,
Perth 6001, Tel +61 9 381 0600
Western Australia. Fax +61 9 381 1496
__________________________________




From: IN%"russel@fox.vut.edu.au" 1-SEP-1994 04:35:12.42
To: IN%"nancy.hamilton@cobra.uni.edu"
CC:
Subj: flock of birds


There are other similar systems around that measure 3D information in real-time
such as polhemus sensors (similar to flock of birds), opto track, etc. that
a basically hardware systems. The thing that you were impressed with I think
was the graphics, that would have been developed separate to the flock of birds
(probably). I would be very interested if you can find out what the software
used was and where it came from. All the hardware systems named above require,
as you noted, cables. There is one system available now that requires no
cables. That is the PRIMAS system from The Netherlands (it is very new). We
are developing similar software to what you saw (real-time) for the PRIMAS
which is why I am so interested.

I can put you in contact with the PRIMAS group if you are interested. Also,
how do you know that the graphics were generated in real-time? Often what
happens is the hardware measures things in real-time, hence the real-time
label,
but in reality the graphics is generated post-event and superimposed of the
original image.

Interesting area, I hope you spark some discussion.

Russell Best

Return-path:



From: IN%"REDFERN@vms.cis.pitt.EDU" 1-SEP-1994 08:22:41.06
To: IN%"Nancy.Hamilton@cobra.uni.edu"
CC:
Subj: RE: Saw a new system

Nancy,
We have been using the Flock of Birds for a year now. We have found it to
be very accurate, but a little tricky to use. The company that sells it is
Ascension Technologies out of Burlington, VT. The phone number I have for them
is (802) 655-7879.

Good Luck,

Mark Redfern, PhD
Human Movement Analysis Laboratory
(412) 647-7923
(412) 647-8720 FAX



Hello Nancy

I have met someone who developed a movement monitoring system (without
videos and cables) which has been used in some hospitals and research
institutions in England (UK) . I am sure he will be able to give you the
details you are looking for. He has been marketing the product himself.
Here is his name and address:

David Mitchelson
Charnwood Dynamics Ltd.
17 South Street
Barrow on Soar
Leics. LE12 8LY
England, UK

Tel:+44 509 620388
Fax:+44 509 236953

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Dr B Serpil Acar
Department of Computer Studies,
Loughborough University of Technology
Loughborough, Leics.
LE11 3TU
ENGLAND

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tel: +44 1509 222 879 fax: +44 1509 211 586 e-mail: S.Acar@lut.ac.uk

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