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Posted by Favne Reas on September 9, 2005, 11:18 pm
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Hello Everybody,
I want to get expert opinions about how we can find/measure the position of
a few millisecond long laser spot on an A4 size of target area.
Although my application notting to do with shooting, using the "laser target
shooting" analogy will help. In these days we can buy small red laser diodes
just for few dolars. Assume we have one of them. The Laser diode will be
connected to a microcontroller which will trigger (turn on and off for few
millisecond) the diode. (If required, I think we can also modulate the laser
diode for few KHz ).
We will point this laser and trigger to a target area of approximatelly
20x30 cm in size and at a distance of 25-50meters. Now the question; on the
target, how we can find the position of this laser spot?
I know there are some laser shooting targets which practically doing this.
How they work?
Thx.
Favne Reas
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Posted by JGCASEY on September 10, 2005, 12:01 am
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Favne Reas wrote:
> Hello Everybody,
>
> I want to get expert opinions about how we can find/measure the position of
> a few millisecond long laser spot on an A4 size of target area.
>
> Although my application notting to do with shooting, using the "laser target
> shooting" analogy will help. In these days we can buy small red laser diodes
> just for few dolars. Assume we have one of them. The Laser diode will be
> connected to a microcontroller which will trigger (turn on and off for few
> millisecond) the diode. (If required, I think we can also modulate the laser
> diode for few KHz ).
>
> We will point this laser and trigger to a target area of approximatelly
> 20x30 cm in size and at a distance of 25-50meters. Now the question; on the
> target, how we can find the position of this laser spot?
>
> I know there are some laser shooting targets which practically doing this.
> How they work?
>
> Thx.
>
> Favne Reas
http://www.philohome.com/sensors/lasersensor.htm
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Posted by Favne Reas on September 10, 2005, 10:05 am
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>
> http://www.philohome.com/sensors/lasersensor.htm
>
Thank you for the link. I liked their "Laser Target Finder Sensor". The
content of this link is fantastic. It explains their system in very good
details. Also the small movie file demonstrates its use.
But, my application is slightly different. I need to know the location of
the laser beam pulse on the target with 5-10mm accuracy. As one suggested
may be a high speed camera would be usefull. But if we try to identify only
the coded/modulated laser rather than any red light, than I tink we need to
have something else or something additional to high speed camera.
Any suggestion?
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Posted by Randall Nortman on September 10, 2005, 10:33 am
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> But, my application is slightly different. I need to know the location of
> the laser beam pulse on the target with 5-10mm accuracy. As one suggested
> may be a high speed camera would be usefull. But if we try to identify only
> the coded/modulated laser rather than any red light, than I tink we need to
> have something else or something additional to high speed camera.
1. Turn the laser on.
2. Capture a frame from the camera, call this image A.
3. Turn the laser off.
4. Capture a frame from the camera, call this image B.
5. C = A - B (pixel by pixel difference)
6. Apply a little fuzzy matching to identify the red spot in C.
Essentially, what I'm suggesting is to forget about modulating or
coding the laser signal, except to the extent that turning it on and
off in sync with the frame rate of the camera can be considered
modulation. Step (6) is where the magic is, but if your camera is
decent and the elapsed time between (2) and (4) is minimal, it should
be pretty easy. If you put a filter on the camera that's matched to
the wavelength of your laser, you're almost certain to get it right in
the absence of malicious attempts to fool the sensor. You won't be
able to have multiple sensors operating at the same time with the same
field of view, unless they are tightly coordinated or use different
wavelengths.
--
Randall
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Posted by Roger Hamlett on September 10, 2005, 10:58 am
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> [...]
>> But, my application is slightly different. I need to know the location
>> of
>> the laser beam pulse on the target with 5-10mm accuracy. As one
>> suggested
>> may be a high speed camera would be usefull. But if we try to identify
>> only
>> the coded/modulated laser rather than any red light, than I tink we
>> need to
>> have something else or something additional to high speed camera.
>
> 1. Turn the laser on.
>
> 2. Capture a frame from the camera, call this image A.
>
> 3. Turn the laser off.
>
> 4. Capture a frame from the camera, call this image B.
>
> 5. C = A - B (pixel by pixel difference)
>
> 6. Apply a little fuzzy matching to identify the red spot in C.
>
> Essentially, what I'm suggesting is to forget about modulating or
> coding the laser signal, except to the extent that turning it on and
> off in sync with the frame rate of the camera can be considered
> modulation. Step (6) is where the magic is, but if your camera is
> decent and the elapsed time between (2) and (4) is minimal, it should
> be pretty easy. If you put a filter on the camera that's matched to
> the wavelength of your laser, you're almost certain to get it right in
> the absence of malicious attempts to fool the sensor. You won't be
> able to have multiple sensors operating at the same time with the same
> field of view, unless they are tightly coordinated or use different
> wavelengths.
In fact the exact 'inverse' of this approach, was what was used for the
early raster scan display 'light pen' systems, where a bright spot was
scanned across the display, and when the pen 'saw' the spot, the X,Y
coordinates where the detector in the pen was pointed could be estimated.
The approach outlined, lends itself to simply synchronising the laser to
the frame sync pulse, activating the laser on alternate frames. Then the
point with the largest change between alternate frames, is the image of
the point where the beam is pointing. The faster the camera sync rate, the
faster the detection can be, and the better the rejection of other
sources. At the 'crude' end of the design, you could even ignore
complexities in matching, and do a direct frame to frame compare.
Best Wishes
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>
> I want to get expert opinions about how we can find/measure the position of
> a few millisecond long laser spot on an A4 size of target area.
>
> Although my application notting to do with shooting, using the "laser target
> shooting" analogy will help. In these days we can buy small red laser diodes
> just for few dolars. Assume we have one of them. The Laser diode will be
> connected to a microcontroller which will trigger (turn on and off for few
> millisecond) the diode. (If required, I think we can also modulate the laser
> diode for few KHz ).
>
> We will point this laser and trigger to a target area of approximatelly
> 20x30 cm in size and at a distance of 25-50meters. Now the question; on the
> target, how we can find the position of this laser spot?
>
> I know there are some laser shooting targets which practically doing this.
> How they work?
>
> Thx.
>
> Favne Reas