Detect direction of motion

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hi,

Could I use ultrasonic or light sensor or anything else to detect
direction of 2D motion including left/right and up/down? I need to
know the exact direcion.

Thanks!

Re: Detect direction of motion

Quoted text here. Click to load it

Yes (and obviously so, since you included "anything else" in the list
of possible options ;-).  But it'll all depend on whether you want to
measure motion in a closed room, or out in the open.  Without walls to
reflect sound or light off, or some other feature that can be observed
to change, it's essentially impossible to measure movement.

But does any of this have to do with algorithms of computer graphics?


--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Detect direction of motion
Quoted text here. Click to load it


The device could be used outdoor or indoor.

But not totally dark envirnment

Re: Detect direction of motion

Quoted text here. Click to load it

That doesn't give the necessary information.  Let me show you why:
imagine your device is were to use an optical pattern-recognition
(rather than signal echo timing) based method.  If you try to use that
device outdoors, and 'outdoors' just happens to be right in the middle
of one of the salt seas of Utah, it'll fail completely, because the
environment will look exactly the same, no matter how fast it moves.

Ultimately, you need something external to the object that specifies
what "being at rest" means to your device, because physics doesn't
provide you with any such thing.  That's what Einstein's Principle of
Relativity really says: there's no such thing as absolute speed (and
thus no way to measure it, either).  So you have to measure speed
relative to *something*, and the device must be able to determine
where this "something" is.

Optical pattern recognition would work in some cases (like in the
optical mouse you may have attached to your computer), ultrasound can
work, too (or bats wouldn't manage to catch anything at night).

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Detect direction of motion
Quoted text here. Click to load it

If you need only direction after a change in direction, use a 2D
accelerometer.

--
------------------------------------------------------------
Creepy, Soulless Gigolo for President ? NOT !
We've slightly trimmed the long signature. Click to see the full one.
Re: Detect direction of motion
On 8 Aug, in article
Quoted text here. Click to load it

Yes.

Oh you want a more detailed answer, without more details especially
about the object, distances, response time, frequency of results, and
environment no more details can be given.


--
Paul Carpenter        | snipped-for-privacy@pcserv.demon.co.uk
<http://www.pcserv.demon.co.uk/ Main Site
We've slightly trimmed the long signature. Click to see the full one.
Re: Detect direction of motion
Quoted text here. Click to load it

How about a 3D inertial measurement sensor? Not cheap but it should do the
job..
http://www.xsens.nl /

Rob



Re: Detect direction of motion
On Mon, 9 Aug 2004 15:50:18 +0200, "Rob Turk"

Quoted text here. Click to load it

   Is there any way to focus those little optical mouse sensors on
infinity (or a couple of feet on out to infinity)? I would think those
would work well against a fixed background, and they're cheap.

Quoted text here. Click to load it

-----
http://mindspring.com/~benbradley

Re: Detect direction of motion
Quoted text here. Click to load it

No. This does not work when light is insufficient.

Re: Detect direction of motion

Quoted text here. Click to load it


The more complicated solution would be accelerometers and laser gyroscopes
to computer distance moved.  Bloody complex if u ask me though I've never
done it myself.



Re: Detect direction of motion

Quoted text here. Click to load it

Not just more complicated, but probably unusable unless I misread the
original question.  An accelerometer can't actually measure velocity
--- if it could, it'd be called a velocimeter.  You can deduce speed from
accelerometer readings, sure, but only if you add

1) highly accurate summation of acceleration over time
2) regular calibration to tell the device what its current speed
   really is, to serve as starting value for the integrator.

IOW: without a separate method to measure speeds, an accelerometer
can't measure speed at all (nor position, for that matter).  A
classical chicken-and-egg situation.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Detect direction of motion
Quoted text here. Click to load it

Unless I misread it, it asked only about direction.

Quoted text here. Click to load it


--
------------------------------------------------------------
Creepy, Soulless Gigolo for President ? NOT !
We've slightly trimmed the long signature. Click to see the full one.
Re: Detect direction of motion
Quoted text here. Click to load it

It asked about direction of *motion*. Not direction of acceleration.
An accelerometer can only measure the magnitude and direction of the
_acceleration_ (delta v) vector.

You have to integrate acceleration over time to get velocity, and you
have to know what the starting value of velocity was.

Re: Detect direction of motion
Quoted text here. Click to load it

That's why my response from 3 days ago read:

    If you need only direction after a change in direction, use a 2D
    accelerometer.

If you model velocity as a vector, a change in direction will register
an acceleration (delta v or force) without a change in magnitude (velocity).
This requires a little understanding of Newton's 1st and 2nd laws of motion.
It's why you get pushed sideways when driving around a radius at constant
linear velocity.

If you want to pop in at an arbitrary slot in time and determine direction
without any history, that is maybe the problem at hand. A poorly stated problem
results in many interesting threads sometimes, where a consisely stated problem
causes useful and terse responses. If you want to increase the volume of C.A.E.,
encourage poorly stated questions.


--
------------------------------------------------------------
Creepy, Soulless Gigolo for President ? NOT !
We've slightly trimmed the long signature. Click to see the full one.
Re: Detect direction of motion
Quoted text here. Click to load it

What is the theory behind, using what sensors?

Site Timeline