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findCirclesGrid unstable row order

asked 2014-03-10 11:58:16 -0500

johnnyz86 gravatar image

updated 2014-03-10 11:58:51 -0500

I'm trying to use findCirclesGrid but it appears to switch the ordering of the points that it returns to me randomly:

correct order

weird order

I'm generating the positions going into drawChessboardCorners as described on OpenCV's camera calibration page

This is running through ROS groovy's latest version on 12.04, using OpenCV 2.4.6.1. I'm having no problem with findChessboardCorners

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answered 2014-03-14 04:51:06 -0500

It looks like your problem is that the target has rotational symmetry. So if you rotate 180 degrees it'll look the same. That's what OpenCV is doing, it has no way of telling which way is up or down, so it will flip the order now and then.

You can fix it by add one extra column giving you a 4x9 target. Or you could black tape over a column giving you 4x7. But more points are typically best.

The answer to this question has quite a good description of doing a good calibration. Although some might be a bit over-the-top depending on your needs.

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Asked: 2014-03-10 11:58:16 -0500

Seen: 962 times

Last updated: Mar 14 '14