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Measuring with a line laser

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Pass1

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Hi all,

I am working on a project where we are doing aerial 3D reconstruction of urban areas. Right now we are using structure from motion with a bunch of pictures, but we want to experiment with lasers.

We want to shine 1 or 2 lines from the quadcopter, record them with a video camera and detect divergence from a straight line and figure out distance.

I was looking at the wicked lasers (the 1.4W one) but after reading the reviews in this forum it is really a mixed bag, some people love them and some people hate them.

So the requirements are:

Needs to be seen 100m away (at night) when stretched as a line from a camera.
Needs to be able to withstand vibrations and minor knocks.
Shouldn't weigh more than half a kg
Less than 1000$usd would be nice.
If it easy to mount even better.

Here is some of the results we are getting, and want to improve upon.
Reconstructing urban areas with a quadcopter flown FPV - YouTube

Thanks!
 





norbyx

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Well I think that what you need is a green laser. With a 200mw laser you will have more than enough power to see it from very far away. Jet lasers has some fine units you can buy.
 
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norbyx said:
Well I think that what you need is a green laser. With a 200mw laser you will have more than enough power to see it from very far away. Jet lasers has some fine units you can buy.
Click to expand...

Even if stretched out as a line?
 
norbyx

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I get your point.... well the answer is easy... you need a laser, green is the best color for what you are looking for... there are two issues that have to be considered very well.

Even if $1000 will buy you a much more powerfull laser (you could get almos a 1W green for that money) the main problem is the weight. The higher the power the more heatsink is needed the bigger batteries need to be to keep it running.

Now consider this
A green color laser will be about 3 times more visible than the same power blue.

You might look at the best laser your quad-copter will allow you to pull up. But be carefull, a 1W laser will eat through batteries very fast.
 
Speedy78

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If the laser is being observed from a camera then you would have to find the wavelength tthat the camera picks up the best. This may even be in the ir spectrum. Green is the most visible to humans not necessarily a camera. My hex csn lift 11 poubds after the 8000mAh battery do if you have something similar you shouldnt have to worry about weight of a a heat sink. You can even power the driver using the battery for the quad. You will lose some flight time due to extra power consumption but no more than you would adding a bunch of other batteries due to the weight.
 
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Thanks for all the replies!

The hexacopter we are building is designed to lift up 3 Sony NEX7, so I think I will substitute one or two of them with the laser equipment

Do any of you experiment with the technology? Maybe you speedy78?
 
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Speedy78

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I have never done any sort of ground mapping. Im all about just hanging cool things off of it and flying it around. You can can some very smakl bosrd cameras and that will help out with the weight a bit.
 
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Cyparagon said:
I don't follow the reasoning here. Care to elaborate?
Click to expand...

Sure!

Basically, if you shine a horizontal line, and have an observing camera in a different place from the laser, you will see the line "bend" as it hits different objects. By observing the difference between the straight line that you would observe if the surface was flat, and what you actually see you can reconstruct shapes.

This is what DAVID laser scanner does DAVID 3D Scanner but I have camera and laser fixed with respect to each other and no control points. They use fixed camera and object with added control points.
 
Cyparagon

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The observing camera in the different place is what threw me. So you'll have two quads that keep a set distance from each other?
 
Cyparagon

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If my rusty trig serves me well, that won't work at all. The angle isn't large enough. Not unless the pole is several meters which will obviously destabilize the copter.
 
chipdouglas

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not at night time.


norbyx said:
Now consider this
A green color laser will be about 3 times more visible than the same power blue.

You might look at the best laser your quad-copter will allow you to pull up. But be carefull, a 1W laser will eat through batteries very fast.
Click to expand...
 
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Cyparagon said:
^Camera sensitivity doesn't change at night like your eyes do.
Click to expand...

Well, depends how you look at it! The pupil changes size like the baldes on the lens when you change aperture. Then you can change the sensitivity by changing ISO. But that's not the point of flying at night!

We want to fly at night to have the laser be very bright compared to what it is shining on (no sun!).

Regarding trig... I was looking at the xbox Kinect. I couldn't find the distance between the infrared laser and the camera, but that is good for 3.5 meters.

Since we are flying at 75m, I assume I can do 75/3.5*(distance for the kinect) and have a ballpark figure. With a rough estimate... I came to about 1.5 meters.
 
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