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detect breaks in metal fences

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nimasa

New Member
Hello,
Do you have any idea how to detect cuts and breaks in metallic fences from 10-15 meters distance, except image processing?
I'm going to use a drone for that. Is there any sensor I can use here?

P.S. I think using image processing from 10-15 meters distance makes it so complicated to detect the pattern of fences and then detect breaks in between.
Fence pattern may vary and it could include small squares as little as 4x4 cm for each fence to 10x10 cm for another. And I'd like to detect breaks as little as a circle with at least 20 cm diameter.

Thanks in advance
 

alec_t

Well-Known Member
Most Helpful Member
Provided the drone kept the sensing equipment at a constant distance from the fence and flew parallel to the fence, in theory it might be possible to detect non-uniformity of the fence by bouncing a microwave signal off it and monitoring the echo strength. I doubt that this method would be practical though.
 

Beau Schwabe

Active Member
P.S. I think using image processing from 10-15 meters distance makes it so complicated to detect the pattern of fences and then detect breaks in between.
.... Not if there is a way to use two cameras or two sections of the same image from a single camera and do a common mode rejection in the image. If you align the images so that pitch of the fence matches on a "good" section of fence, then moving to a break in the fence should show a spike in the signal to noise ratio. A simple way to do common mode rejection is to XOR the two images you are comparing. By XORing the two images all common mode data will drop off, and you are only left with the differences between the two images. You might have to roll your own code, but something like VisualBasic could even perform that type of operation on an image without too much headache.
 

dknguyen

Well-Known Member
Most Helpful Member
Are these solid fences or wire fences? How big is your budget and weight limit?

If you can handle $2000+ and about 1 lbs or 500g, you can use a scanning LIDAR:

Examples:
http://www.robotshop.com/en/hokuyo-ust-10lx-scanning-laser-rangefinder.html
http://www.robotshop.com/en/hokuyo-ust-20lx-scanning-laser-rangefinder.html#Specifications

But even those are just line scanners and 3D scanning is what you really want but that's even more cost prohibitive.

There is this one but it is right on the border of your range limit so I don't know how reliable it would be, but it is 1/4 of the cost:
http://www.robotshop.com/en/rplidar-a2m6-360-laser-scanner-16-m.html

Does it also have to be a drone? I mean...it's a fence and you're looking at it from the side. It can't be an ground ROV? That would simplify processing speeds, stability, and payloads, etc quite a bit

If it's a wire fence though...that'd be tough...
 
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Colin

Active Member
It is very easy. Fit a very thin insulated wire along to the top of the fence and secure it at ever 300mm. Connect the far end to the fence and use a closed loop detector.
 

ronsimpson

Well-Known Member
Most Helpful Member
Fence pattern may vary and it could include small squares as little as 4x4 cm for each fence to 10x10 cm for another. And I'd like to detect breaks as little as a circle with at least 20 cm diameter.
I think the wire is like this picture. You are looking for a hole or brake in the fence. So not easy.
upload_2017-9-23_19-31-58.jpeg
If the picture was as clear as this picture, I would try counting how many wires there is across the picture. OR Wires/meter. AND count five times across the picture.

Where the chickens are it will be hard to see the wire. So missing one wire will be typical.
 
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