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Posted by on May 5, 2008, 2:17 pm
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Is it possible to build the following scenario, and if so, can anyone
point me on the right track?
I have a person and I want to place small transceivers in various
places on his body. The transceivers would all be able to detect
their distances from each other using some sort of wireless
transmission and then send those distances to a small wireless
processor attached to the person's hip. The processor would then use
the distance variables to determine the relative positions of each
transceiver in 3-dimensions.
I've tried to research this and I've found a lot of sensors that can
determine distances to a random object in its field of vision. But I
would like to know the distance between 2 discrete objects that both
move around. I was thinking maybe I can send a wireless transmission
with a timestamp and a serial number and then the receiving device
would record that information along with the current time stamp.
Maybe the transmission time could then be used to calculate the
distance?
Are there currently transceiving devices that can do this? I am less
concerned about the processing and mostly concerned about the data
capturing.
Thank You.
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Posted by cadcoke4 on May 5, 2008, 3:25 pm
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On May 5, 1:17=A0pm, mattrapop...@gmail.com wrote:
> I have a person and I want to place small transceivers in various
> places on his body. =A0The transceivers would all be able to detect
> their distances from each other using some sort of wireless
The "time of flight" for wireless, as you propose, is going to be very
difficult because electro-magenetic waves (speed of light) are
extremely fast. So, I woudl abandon that idea. But, sound is an
alternative. If each transceiver takes turns emitting an ultrasonic
"ping", then each of the other transceivers can record the time it
takes for the sound to travel to them. But, you also need to let each
transciever know when the pulse was emitted by either a wired or
wireless transmission (an IR beacon is common, but you may not have
line-of sight to do this)
Here is one link to the type of system I am describing, as commonly
used in robotics;
http://www.restena.lu/convict/Jeunes/beacon.htm
In your case, you might send an IR signal (similar to those used in a
TV remote control) to tell a particular beacon to "Ping"... at the
same time the other transcievers read the IR signal to know which
transciever is doing the Ping and start to listen for it.
But, in the above method, you might have issues with some transcievers
not getting the IR signal. But, if you are in a small-ish room, you
can just flood the room with the IR, and it may work. Still, a wired
system is going to be a lot easier to do.
Joe Dunfee
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Posted by John Nagle on May 6, 2008, 12:21 am
Please log in for more thread options mattrapoport@gmail.com wrote:
> Is it possible to build the following scenario, and if so, can anyone
> point me on the right track?
>
> I have a person and I want to place small transceivers in various
> places on his body. The transceivers would all be able to detect
> their distances from each other using some sort of wireless
> transmission and then send those distances to a small wireless
> processor attached to the person's hip. The processor would then use
> the distance variables to determine the relative positions of each
> transceiver in 3-dimensions.
>
> I've tried to research this and I've found a lot of sensors that can
> determine distances to a random object in its field of vision. But I
> would like to know the distance between 2 discrete objects that both
> move around. I was thinking maybe I can send a wireless transmission
> with a timestamp and a serial number and then the receiving device
> would record that information along with the current time stamp.
> Maybe the transmission time could then be used to calculate the
> distance?
>
> Are there currently transceiving devices that can do this? I am less
> concerned about the processing and mostly concerned about the data
> capturing.
>
> Thank You.
Sure. Look up "magnetic motion capture". It's not easy to do, but
it's done routinely.
John Nagle
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Posted by Gordon McComb on May 6, 2008, 3:00 pm
Please log in for more thread options In case you are attempting to use this for motion capture, probably the
best place to start is the wide variety of technical articles regarding
motion capture systems used for such things as movie special effects,
medical research, etc.
Maybe you need all these transceivers, or maybe what you can really use
is a jogging suit with (for example) triggered LEDs or fluorescent pads
embedded in it, and shot by a high-resolution digital camera. Motion
capture software translates the markers into distance and movement, and
can export that data for such things as integration with Maya or another
character animation program. You get what you are looking for (distance
between two objects) but of course this system only works for objects
visible to the camera.
John mentions magnetic AC trackers, but there's also acoustic and
several other technologies in regular use. Depending on the resolution
you need you might be able to use inertial tracking, like what a Wii
controller does. The solution really depends on how accurate you need to
be, how many frames per second of motion you need to record, and how
many markers you need to monitor.
-- Gordon
mattrapoport@gmail.com wrote:
>
> Is it possible to build the following scenario, and if so, can anyone
> point me on the right track?
>
> I have a person and I want to place small transceivers in various
> places on his body. The transceivers would all be able to detect
> their distances from each other using some sort of wireless
> transmission and then send those distances to a small wireless
> processor attached to the person's hip. The processor would then use
> the distance variables to determine the relative positions of each
> transceiver in 3-dimensions.
>
> I've tried to research this and I've found a lot of sensors that can
> determine distances to a random object in its field of vision. But I
> would like to know the distance between 2 discrete objects that both
> move around. I was thinking maybe I can send a wireless transmission
> with a timestamp and a serial number and then the receiving device
> would record that information along with the current time stamp.
> Maybe the transmission time could then be used to calculate the
> distance?
>
> Are there currently transceiving devices that can do this? I am less
> concerned about the processing and mostly concerned about the data
> capturing.
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Posted by on May 7, 2008, 2:13 pm
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Thank you for the thoughtful responses. I've looked into the
solutions mentioned and unfortunately I don't believe they will suit
my purpose. I realize now how important it was for me to stress the
required accuracy. It should be accurate to the millimeter or better
if possible. It also must be entirely self contained. No cameras.
Onboard processor.
Many Thanks.
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> places on his body. =A0The transceivers would all be able to detect
> their distances from each other using some sort of wireless