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What patern to be detected from far away

asked 2019-05-08 09:41:45 -0500

sandro gravatar image

Hi, I'm trying to use markers on the ground to tell a drone where to land. I started an implementation using QR code, as there is a nice class for it in OpenCV. However, I found out that a QR code needs to be at least 0.1 times the distance between camera and QR code. This would mean that with a 1*1m QR code, we can fly at maximum at 10m above ground, which is very low (there is a non negligeable risk of collision with trees ot buildings)

I'm therefore looking into other paterns I could use instead of QR code, which are easier to recognise from far away.

My main constraints are : - the patern should be recognaseble from as high as possible (ideally 50-60m), but some false positives are OK - Contrary to a QR code, I don't need it to contain any information (there will be only one such patern in the area) - I have to be sure that it is my patern once at lower altitude (at least from 5m distance, ideally 20 or more) : I have to be sure that I will not confuse it with any random object in the area. - the detection (of the center) of the patern has to be done on a raspberry pi in real time (at least 5 times/second), so the detection algorithm needs to be not to slow

Does any of you have an idea which patern to use and how best to detect it (if there is a class for it in OpenCV or another library, it's a plus)?

Thank you very much in advance

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answered 2019-05-11 16:07:34 -0500

Tetragramm gravatar image

Try a simple chessboard pattern. A 2x2 chessboard can be seen from very far away, and the center is the center no matter how close you get.

It's got a detector built into opencv already, and you can increase the size to 3x3 or 4x4 to make it less likely to see false alarms. That would require a bit more processing once you get close to make sure you land at the center, but it shouldn't be hard.

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Asked: 2019-05-08 09:41:45 -0500

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Last updated: May 11 '19