🚀 go-pugleaf

You might also want to try the new miniature Gyro (sorry: no address)
if you can tolerate one degree per minute drift. Also, there are one or
two 3-D mice out there, one I think from Logitech.
 --------------------------------------------------------------------------
| lord snooty @the giant | wolfpack, silver, down to the water             |
| poisoned electric head |              andrew palfreyman@cup.portal.com   |
 --------------------------------------------------------------------------

In article <1992Apr7.031033.19729@njitgw.njit.edu> andrews@rehab.njit.edu (John Andrews) writes:
>     I am starting a project that requires me to locate and
>     track a device in 3-space.

 [stuff deleted]

The way I would do this is by using ultrasound.  Construct an imaginary
cube around the space you need to track the object.  In the center of each
of three non-parallel faces you put an ultrasound transducer (mike).

The object emits a short pulse of ultrasound every, say, 1/100 sec.  Then
you just see how long it takes the sound to get to each mike.  The equations
to find the location of the object should be easy.  

Using v=330 m/s, even just 1 MHz timing resolution will give you the location
accurate to 0.3 mm.  

Of course, the object will have to be attached by a little wire, unless you
want to use radio to synch everything up.



-- 
Johan Thornton
(but my friends call me jthornto@ee.ubc.ca)

In article <1992Apr8.005925.455@ee.ubc.ca>, jthornto@ee.ubc.ca (Johan
Thornton) writes:
|> In article <1992Apr7.031033.19729@njitgw.njit.edu>
andrews@rehab.njit.edu (John Andrews) writes:
|> >     I am starting a project that requires me to locate and
|> >     track a device in 3-space.
|> 
|>  [stuff deleted]
|> 
|> The way I would do this is by using ultrasound.  Construct an
imaginary
|> cube around the space you need to track the object.  In the center of
each
|> of three non-parallel faces you put an ultrasound transducer (mike).
|> 
|> [stuff deleted]
|> 
|> Using v=330 m/s, even just 1 MHz timing resolution will give you the
location
|> accurate to 0.3 mm.  
|> 
   [stuff deleted]

The accuracy of such a measuring system will also be limited by the
wavelength of the ultrasound (US). Let us assume that the
we need one full wave for reliable detection and that we are operating
at 250 kHz. Tperiod=4 us, v=330 M/s, Lambda
(wavelenght)=Tperiod*v=0.00132 m (1 mm).
You might be able to detect within less than one wavelenght,
but usually in US there is plenty of noise around and the detection
circuitry introduces errors of this kind.

Additionally v is dependant on teperature, you probably want to measure
it (temperature) and compensate for it in you calculations.

250 kHz is, I believe, the highest frequency
you will find being used, higher than that the dissipation in air
starts becoming a problem

Sjur Vestli

In article <1992Apr14.094205@andrea-doria.ifr.ethz.ch> vestli@andrea-doria.ifr.ethz.ch (Sjur Jonas Vestli) writes:
>|> 
>|> Using v=330 m/s, even just 1 MHz timing resolution will give you the
>location
>|> accurate to 0.3 mm.  
>|> 
>
>The accuracy of such a measuring system will also be limited by the
>wavelength of the ultrasound (US). Let us assume that the
>we need one full wave for reliable detection and that we are operating
>at 250 kHz. Tperiod=4 us, v=330 M/s, Lambda
>(wavelenght)=Tperiod*v=0.00132 m (1 mm).
>You might be able to detect within less than one wavelenght,
>but usually in US there is plenty of noise around and the detection
>circuitry introduces errors of this kind.
>
> Sjur

And why do you say that measurement resolution is limited by wavelength
and noise?  We're talking delay estimation here, not optics.  Radar
people know how to design waveforms with good correlation properties.
I'm not a radar person, but I don't see why you can't get arbitrarily
good resolution using chirps.

As for noise, just average your measurements.  If this 3D tracker is
following hand motions, 10-20 measurements/sec should be sufficient.
Use a rep rate of 1000-2000 pulses/sec, and average 100 pulses for each
reading.
-- 
   Dave Kemp   dpkemp@afterlife.ncsc.mil              "Pave the Bay!"
   #include <std/disclaimer>

In <1992Apr7.031033.19729@njitgw.njit.edu> andrews@rehab.njit.edu (John Andrews) writes:
>     I am looking at using a 3-SPACE digitizer from Polhemus
>     (also called ISOTRACK, Kaiser Aerospace) and am looking
>     for any information on this system or perhaps similar
>     systems from competing companies.

I bought one of these systems for my research several months ago.
It works well but is very sensitive to electronics/metal objects in the
area.  The software that comesw with it is pretty lame.  You have to 
write your own code (in C) to use it to do anything useful.  It is being
used in a variety of applications, not just VR.

The Isotrak gives location (x,y,z) AND orientation (pitch, roll, yaw) for 
a total of 6 degrees of freedom.  I don't see how you could get all that
using ultrasound (especially the 3 angles).

>     Has anyone any experience with this? Somethign similar?
>     A better way to locate and track something in 3 dimen-
>     sions? This system will run me over $10,000, so any and
>     all responses greatly appreciated.

No way. The base system (1 source and 1 probe) goes for about $3300.  
If you ask them right, who can buy a used sytem (same warantee) for half
that.  

If you want more info, let me know.

mike

-- 
Michael Drues                              Dept. of Biomedical Engineering
Internet:drues@iastate.edu                        1146 Veterinary Medicine
BITNET:v2.med@isumvs.bitnet                          Iowa State University
Office:(515)294-6520(or 4-1771) Home:(515)233-5652        Ames, Iowa 50011

drues@iastate.edu (Michael E Drues) writes:

>In <1992Apr7.031033.19729@njitgw.njit.edu> andrews@rehab.njit.edu (John Andrews) writes:
>>     I am looking at using a 3-SPACE digitizer from Polhemus
>>     (also called ISOTRACK, Kaiser Aerospace) and am looking
>>     for any information on this system or perhaps similar
>>     systems from competing companies.

>I bought one of these systems for my research several months ago.
>It works well but is very sensitive to electronics/metal objects in the
>area.  The software that comesw with it is pretty lame.  You have to 
>write your own code (in C) to use it to do anything useful.  It is being
>used in a variety of applications, not just VR.

>The Isotrak gives location (x,y,z) AND orientation (pitch, roll, yaw) for 
>a total of 6 degrees of freedom.  I don't see how you could get all that
>using ultrasound (especially the 3 angles).

>>     Has anyone any experience with this? Somethign similar?
>>     A better way to locate and track something in 3 dimen-
>>     sions? This system will run me over $10,000, so any and
>>     all responses greatly appreciated.

>No way. The base system (1 source and 1 probe) goes for about $3300.  
>If you ask them right, who can buy a used sytem (same warantee) for half
>that.  

>If you want more info, let me know.

You may want to check out a company called Ascension Technology, P.O.
Box 527, Burlington, VT  05402. Phone (802)655-7879, FAX (802)655-5904.

They also make an electronic 6-degree of freedom tracker.  I used one
of their prototypes for a demo and I give pretty good accuracy.  It 
is also insensitive to large conducting surfaces (I put an aluminum
pop can right in the middle of the setup without problems).  It is 
still sensitive to ferrous material though.


--
Larry                                   |   Thunder makes all the noise;
                                        |   lightning gets the job done.
larryd@milton.washington.edu
I have my opinion; the university has its own.

In article <drues.703291186@pv320a.vincent.iastate.edu> drues@iastate.edu writes:
>In <1992Apr7.031033.19729@njitgw.njit.edu> andrews@rehab.njit.edu (John Andrews) writes:
>>     I am looking at using a 3-SPACE digitizer from Polhemus
>>     (also called ISOTRACK, Kaiser Aerospace) and am looking
>>     for any information on this system or perhaps similar
>>     systems from competing companies.
>
>I bought one of these systems for my research several months ago.
>It works well but is very sensitive to electronics/metal objects in the
>area.  The software that comesw with it is pretty lame.  You have to 
>write your own code (in C) to use it to do anything useful.  It is being
>used in a variety of applications, not just VR.
>
>The Isotrak gives location (x,y,z) AND orientation (pitch, roll, yaw) for 
>a total of 6 degrees of freedom.  I don't see how you could get all that
>using ultrasound (especially the 3 angles).
>
>>     Has anyone any experience with this? Somethign similar?
>>     A better way to locate and track something in 3 dimen-
>>     sions? This system will run me over $10,000, so any and
>>     all responses greatly appreciated.
>
>No way. The base system (1 source and 1 probe) goes for about $3300.  
>If you ask them right, who can buy a used sytem (same warantee) for half
>that.  
>
>If you want more info, let me know.
>
>mike
>
>-- 
>Michael Drues                              Dept. of Biomedical Engineering
>Internet:drues@iastate.edu                        1146 Veterinary Medicine
>BITNET:v2.med@isumvs.bitnet                          Iowa State University
>Office:(515)294-6520(or 4-1771) Home:(515)233-5652        Ames, Iowa 50011



This is true. I should have mentioned I don't need the 3d positition of a *point* in 
space but of a *plane*, which requires the additional degrees of freedom. That is
where the Polhemus was useful (as are a few other systems).

But system latency is a problem with Polhemus, from what I have been told. It is too slow
for tracking most movement.

As for your pricing, the 3300 is for a single-sensor, and I need more than that. I need to
make referenced measurements, so I need the two -sensor-input system, which runs $9900
plus the $900 for the additonal sensor. It is an expensive system.

Referenced measurements also demand more of the system latency, enhancing the problem
with Polhemus.

									-=john

-- 
-----------------------------------------------------------------------------
john f andrews                SYSOP           The Biomedical Engineering BBS
    24 hrs             300/1200/2400/4800               (201) 596-5679
-----------------------------------------------------------------------------

In article <drues.703291186@pv320a.vincent.iastate.edu> drues@iastate.edu writes:
>
>The Isotrak gives location (x,y,z) AND orientation (pitch, roll, yaw) for 
>a total of 6 degrees of freedom.  I don't see how you could get all that
>using ultrasound (especially the 3 angles).
>


Actually, it's quite simple.  Using three sound sources located sufficiently far apart
will tell you the object's location and orientation.  And if you only need the 
orientation of a plane, two sources are sufficient.


-- 
Johan Thornton
(but my friends call me jthornto@ee.ubc.ca)

In article <1992Apr17.000653.4251@ee.ubc.ca> jthornto@ee.ubc.ca (Johan Thornton) writes:
>In article <drues.703291186@pv320a.vincent.iastate.edu> drues@iastate.edu writes:
>>
>>The Isotrak gives location (x,y,z) AND orientation (pitch, roll, yaw) for 
>>a total of 6 degrees of freedom.  I don't see how you could get all that
>>using ultrasound (especially the 3 angles).
>>
>Actually, it's quite simple.  Using three sound sources located sufficiently far apart
>will tell you the object's location and orientation.  And if you only need the 
>orientation of a plane, two sources are sufficient.

The key difference with the Isotrak, an electromagnetic system, is
that the three sources are co-located on different perpendicular
axes.  The sensor has the same arrangement (reciprocity applies).
Thus, in each sampling cycle, nine measurements are taken to determine
position and location.

--
Brian Hanafee                         Advanced Decision Systems
bhanafee@ads.com                      1500 Plymouth Street
(415) 960-7300                        Mountain View, CA 94043-1230