DIY Laser levelling using webcam and laser level

[Sasquatch]

Jar from GitHub loads on Ubuntu, detects max resolution as 640x480 then fails. i'm getting blank window and null pointer exception in NextFrame method.

Built from GitHub source on Ubuntu runs ok, detects max resolution as 640x480.

It is indeed driver issue, apparently there is no single driver working on all platforms, those working in Windows/Linux won't work on Mac. And those working on MAC/Linux won't work on Windows.

Just make an option in preferences to select resolution. People using that kind of software should be techie enough no know how to check max supported resolution of their camera?

Did some testing today. SJ4000 gives resolution of 3.75um per pixel in 1280x720 video mode. 4.8mm active sensor width.
If LaserLevel could work with stills, I could get 1.2um per pixel from that camera. Waaay too sensitive, or is it?

[Sasquatch]

My laser finally arrived, and...judge yourself.
camera fitted in precision vice riding on grade 00 18"x 24" granite.
Running across the beam i'm getting 0.04mm deviation from straight line on ~500mm distance
Running away from laser I'm getting 0.02mm deviation on ~500mm distance.
Beam is changing width and apparently this change is not symmetrical.
I was getting same results with pointer laser(runnig away from it), but assumed that irregular dot with surrounding artefacts was to blame.
It's still viable way of checking linearity, but as shadow camera and wire. Cheap(£25, glass lens, 80 MW) lasers are not precise enough. maybe £500 line laser could be used, but for such money there's plenty other options.

[Sasquatch]

My laser finally arrived, and...judge yourself.
camera fitted in precision vice riding on grade 00 18"x 24" granite.
Running across the beam i'm getting 0.04mm deviation from straight line on ~500mm distance
Running away from laser I'm getting 0.02mm deviation on ~500mm distance.
Beam is changing width and apparently this change is not symmetrical.
I was getting same results with pointer laser(runnig away from it), but assumed that irregular dot with surrounding artefacts was to blame.
It's still viable way of checking linearity, but as shadow camera and wire. Cheap(£25, glass lens, 80 MW) lasers are not precise enough. maybe £500 line laser could be used, but for such money there's plenty other options.

[devmonkey]

Do you have any pics of your laser and sensor? I think there is something strange going on with your setup if you see errors moving the sensor along the laser axis. Is the laser spreading? Have you removed all optics and filters from the sensor and bolted the pcb to something solid? We do know that the laser beam is not bending in the air so something else is wrong.

[Sasquatch]

Bare sensor, unless there is anti aliasing filter glued to silicon, but AFAIK it's DSLR's area.
Stripping further is not really an option, not usable as shadow camera as there are modular PCB's perpendicular to the sensor sticking above it's surface. Webcam incoming.



Cable is clamped, moving laptop around has no impact on measurements when camera is stationary.

Thinking about it makes no sense.
Both lasers are focusable, both are set to project same width/size line/dot at 8 meters and 20 cm.
They might be represented as

Laser diodes are not perfect, if one edge is brighter (double line above) average brightness will still be straight line
Pointer produces coupe stray beams right next to the main point, that could be source of the problem.
with line laser i have no idea.

[devmonkey]

It could be aliasing from reflections on the lens holder thread, I got much better results with the sensor mounted with nothing close to it in the near field. See picture below, that window started off as a 6mm round hole, it caused aliasing hence I opened it up so no reflected laser light could hit the sensor.

I don't know much about dslrs but maybe it could have lens distortion correction built in which would be warping the image non-linearly across the sensor. Have you got a cheap web cam to try with? It is also unlikely that sensor pcb is hard fixed to the body, the ones i've take apart are usually on soft mounts that let the board move around to absorb shocks.

[Sasquatch]

It's cheap Sj4000 clone distortion is massive, if there is correction it does very bad job. I have cheap webcam and 0.08mm steel wire on order. Will try both laser and wire to rule out sensor nonlinearity errors.

[devmonkey]

It's cheap Sj4000 clone distortion is massive, if there is correction it does very bad job. I have cheap webcam and 0.08mm steel wire on order. Will try both laser and wire to rule out sensor nonlinearity errors.

One other thing that occurred to me, how did you ensure you moved the sensor/vice assembly absolutely in a straight line? Any deviation in this procedure would show up as non-linear errors in your linearity measure since it would have been impossible to get the laser perfectly planar with the granite. This applies to both types of laser dot and line. I think you need a precision straight edge as well as the reference surface to check the accuracy of the system.

[Sasquatch]

One other thing that occurred to me, how did you ensure you moved the sensor/vice assembly absolutely in a straight line? Any deviation in this procedure would show up as non-linear errors in your linearity measure since it would have been impossible to get the laser perfectly planar with the granite. This applies to both types of laser dot and line. I think you need a precision straight edge as well as the reference surface to check the accuracy of the system.

I used straight edge clamped to the granite, just as you said.

Cheap webcam arrived, useless with lasers, sensor is smaller than the beam, will test it with wire when it gets here.

[devmonkey]

I used straight edge clamped to the granite, just as you said.

Cheap webcam arrived, useless with lasers, sensor is smaller than the beam, will test it with wire when it gets here.

Sounds like your laser is no good, can you post a picture of it? Even my dewalt laser level produces a line narrower than the VGA sensor.