cheap laser distance range finder with USB output

[Joe Sommer]

 

One of my friends in the construction industry owns

a GM100DU laser distance range finder with USB

output (about $150).  It is remarkably accurate, projects a

moderately bright red laser spot and claims 100m

maximum range.  It appears as a USB Human Interface

Device (HID) under Windows.

 

Unfortunately it only exports distance data over USB

in single measurement mode when you manually press

a button.  It then sends a long string of text at a very slow

baud rate that takes over 30 seconds.  It does not export

continuous distance measurements over USB.

 

I contacted the Chinese manufacturer Benetech to see

if there is some hidden "cheat code" to allow continuous

data export over USB.

 

This is the only laser distance sensor with USB or serial

output that I have tried.  Perhaps some of the others

have continuous data export or faster single measurements.

 

Joe

 

 

[HV]

This one is twice as expensive, but has an update rate of 10 Hz calibrated mode and 200 Hz raw data mode, over RS232.

Opti Logic RS400 OEM Laser Rangefinder $319
http://www.opticsplanet.com/opti-logic-range-finder-rs400.html

 

[HV]

There's also this, but i don't know what it costs:

http://www.autonomoustuff.com/mdl-micro-laser-altimeter-module-mlm.html

[Joe Sommer]

On Thursday, April 11, 2013 9:32:24 AM UTC-4, Joe Sommer wrote:

 One of my friends in the construction industry owns

a GM100DU laser distance range finder with USB

output (about $150).

 

I took the GM100DU outside on a slighty overcast day.

I could see the laser spot and get distance measurements

up to 15 m on my Hetzer.  Beyond that, I could not see

the spot to accurately point the laser.  I could get very

repeatable measurments up to 40m on the side of a

light colored house.

 

When the sun came out, I could not get any measurements

at any range even on the house.  The bright sunlight

overpowered the laser spot.

 

I do not recommend this sensor for electronic firing solutions.

 

Another friend has a golf range sensor with an internal spotting

scope.  I may try mating it with a video camera.  We would then

need some simple image processing to read the seven-segment

range numbers that appear as an ovelay on the scope image.

Joe

 

 

[TyngTech]

I think active sensor tech is a blind alley (get it, blind in bright sunlight... ;-).  Passive is the way to go.  Two pivoting cameras with an image overlay (ie, an optical rangefinder) is the correct path for the hobby and worthy of the efforts by Joe, Doug, and other equally skilled computer boffins.

ST

[Pete Arundel]

And I think that Stadiametric ranging may be worthwhile. Dead simple - all you need it an overlay on your video output. 

Bore sight on the + and all you have to do is bracket your target within the curved stadia lines and the elevation is set correctly. (Note eleveation not set correctly on all but level ground. Trunion tilt is not compensated, nor is vehicle cant. This statement in no way constitutes a definition of fact. For RC tank combat purposes it would be better to calibrate your stadia lines for the front rather than the side of the typical target tank.)

[Doug Conn]

I’m not even sure they’d need to pivot. It would be great not to use moving parts for this if possible. Cheap webcams now have a 1280 pixel horizontal resolution. If you separate two of those, facing straight ahead, by a known distance then you could calculate the physical distance based on the pixel separation of an image feature. I guess you could use any angle of camera mounting as long as it was constant.

 

I ran through this math using the specs from my robot camera. I calculated a maximum range resolution of 360’. Even if my math is way off (which is not unusual) it’s still much farther then we need for a paint ball tank.

 

This sounds like  a fun project. I have too many of those lined up already. If only I didn’t have to WORK for a living I could do so much more tank stuff ! I wish I was a real estate mogul like Steve.

 

-          Doug

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[Joe Sommer]

On Sunday, April 14, 2013 10:54:00 AM UTC-4, Pete Arundel wrote:

And I think that Stadiametric ranging may be worthwhile. Dead simple - all you need it an overlay on your video output.

 

I am beginning to like Pete's recommendation more and more.

This method was used in WWII and is still used for cheap

monocular golf rangefinders.

see eBay item 281021741030

 

I have a 10x gun camera (small video cam mated to10x25

monocular spotting scope) that I brought to TankFest.  However

we did not have time for a demo.

 

I borrowed my friends Nikon Octane golf rangefinder with

6x spotting scope.  I will try to mate it with the video cam.

see eBay item 290870478696

 

Joe

 

[Pete Arundel]

Not sure if the stadia used for a golf rangefinder will help. The one I have (not that I've ever set foot on a golf course . . .) uses the height of the flag as the reference and is graduated to 300 yards / metres. It makes the assumption that all golf flags are the same height which seems to me like a fairly big assumption. 

Anyway, the way I'd do it is to get an old Overhead Projector Pen and some clear film to cover my video screen. Then  fire a paintball into a target a foot or so away, cetre the camera on the resultant splat and mark the screen with a cross to designate the boresight. Next I'd put a box the same width as a 1/6th tank at 10 yards range and shoot at it a few times. When I was happy that the elevation was correct to hit the target at that range reasonably consistently I'd put a dot on each side of the target as seen on the screen. Repeat at 15, 20, 25, 30, 35 yards range. Draw two curves, as smoothly as possible, joining the dots on both sides. 

Done. 

It might even work..

[TyngTech]

"I’m not even sure they’d need to pivot. It would be great not to use moving parts for this if possible. Cheap webcams now have a 1280 pixel horizontal resolution. If you separate two of those, facing straight ahead, by a known distance then you could calculate the physical distance based on the pixel separation of an image feature."

One word..., genius!

ST

[Doug Conn]

Thanks !

 

Now, I guess I HAVE to see if it actually works…

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[Joe Sommer]

On Sunday, April 14, 2013 9:41:02 PM UTC-4, RocketMan wrote:

Now, I guess I HAVE to see if it actually works…

"I’m not even sure they’d need to pivot. It would be great not to use moving parts for this if possible. Cheap webcams now have a 1280 pixel horizontal resolution. If you separate two of those, facing straight ahead, by a known distance then you could calculate the physical distance based on the pixel separation of an image feature.

Doug,

 

Do not bother doing the trigonometry.  You will ultimately

need to measure camera separation distance, focal length

of each camera and lens distortion (barreling, pin cushion)

which can be difficult to do accurately.

 

I will dig out an algortihm that we used  in the bad old days of

photogrammetry called the Direct Linear Transform (DLT).  See

https://me363.byu.edu/sites/me363.byu.edu/files/userfiles/5/DLTNotes.pdf

 

It inherently includes intrinsic camera paramters (focal length

and lens distortion) and extrinsic camera parameters (focal

point location and prinicipal axis orientation).

 

To calibrate, you place a grid of points printed on a flat

plate at several known ranges and measure pixel locations

of the points.  The algoithm then calculates binomial coefficients

that provide simple computation of global locations for

a point that is visible to both cameras.

 

We used it for photogrammetry in biomechanics of human

movement for scientific analyses similalry to multicamera

motion capture for computer generated images in movies

(e.g. Golem in LOTR).

 

Joe

 

[dwco...@comcast.net]

Hi Joe -

 

>>  measure camera separation distance,

Sure. My back of the envelope run through assumed a 6" separation.

 

It seems like most of the other camera parameters you mention go into calculating the camera field of view. That value is published for many webcams. For example, the one I use has a 53 degree horizontal FOV. If you know those values couldn't you calculate distances ? It does ignore lens distoration, and the fish-eye lenses on some webcams would certainly screw things up.

 

I guess if the calculations turned out to be wrong, a system liek this could always be calibrated as you suggest.

 

   - Doug

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From: "Joe Sommer" <anvi...@comcast.net>
To: rctank...@googlegroups.com
Sent: Monday, April 15, 2013 8:13:09 AM
Subject: Re: [TANKS] Re: cheap laser distance range finder with USB output

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[Joe Sommer]

On Monday, April 15, 2013 10:37:18 AM UTC-4, RocketMan wrote:

I guess if the calculations turned out to be wrong, a system liek this could always be calibrated as you suggest.

If you assume that both cameras have the same focal length
and resolution with minimal distortion, the following simplified
equation should work for range significantly longer than horizontal
camera separation.

r = range of target point from center between focal points of cameras [inch, ft, yd, m]
s = horizontal separation between focal points of cameras [inch, ft, yd, m]
d = horizontal distance between the image of the target point in right camera
     and the image of the target point in left camera [pixels]
f = focal length of cameras [pixels]

r = s * f / d

You must measure s accurately with a ruler or caliper.

For focal length in pixels units, you need to know focal length
of the lens [inch or mm units] and physical pixel spacing [inch
or mm units].

Alternately, place the target point at several known range distances
(r_1, r_2 ... r_n) and measure pixel separation distance for each (d_1, d_2 ... d_n).
.
f = sum( r_1*d_1 + r_2*d_2 + ... + r_n*d_n ) / (n*s)

More sophisticated calibrations can handle image center offset,
camera misalignment and lens distortion.

Joe

[TyngTech]

"More sophisticated calibrations can handle image center offset, camera misalignment and lens distortion."

Whats the calculation to handle paintball goo all over the lens?

[Joe Sommer]

On Monday, April 15, 2013 4:27:24 PM UTC-4, TyngTech wrote:

"More sophisticated calibrations can handle image center offset, camera misalignment and lens distortion."

Whats the calculation to handle paintball goo all over the lens?

 

Any tank that carries such a sophisticated fire control system

will need a cloaking device.  Anvilus is currently beta-testing

adaptive IR camouflage from BAE systems.

http://www.youtube.com/watch?v=Pftna34TbJU

 

Fred Simms, Director

Stealth, Targeting and Disinformation (STD)

 

 

[Doug Conn]

Little miniature windshield wipers and squirters ?

 

From: rctank...@googlegroups.com [mailto:rctank...@googlegroups.com] On Behalf Of Joe Sommer
Sent: Monday, April 15, 2013 9:27 PM
To: rctank...@googlegroups.com
Subject: Re: [TANKS] Re: cheap laser distance range finder with USB output

 

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