Camera ChArUco calibration errors

Question

I am trying to calibrate the jevois camera with a 120 degree fisheye lens using this guide: http://jevois.org/tutorials/UserArUcoCalib.html

I have printed out the charuco board on a piece of A4 paper, measuring the ml=17mm, sl=30mm, and running the command:

./calibrate_camera_charuco -d=0 -h=5 -w=8 --ml=17 --sl=30 --rs --sc calibration.yaml

The problem is that after hitting esc to to do the calibration on the pictures I've taken, I usually get this error message:

OpenCV Error: Assertion failed (nCorners > 0 && nCorners == _charucoCorners.getMat(i).total()) in calibrateCameraCharuco, file /build/opencv-L2vuMj/opencv-3.2.0+dfsg/contrib/modules/aruco/src/charuco.cpp, line 703
terminate called after throwing an instance of 'cv::Exception'
  what():  /build/opencv-L2vuMj/opencv-3.2.0+dfsg/contrib/modules/aruco/src/charuco.cpp:703: error: (-215) nCorners > 0 && nCorners == _charucoCorners.getMat(i).total() in function calibrateCameraCharuco

and sometimes this error:

OpenCV Error: One of arguments' values is out of range (The number of points in the view #2 is < 4) in cvCalibrateCamera2Internal, file /build/opencv-L2vuMj/opencv-3.2.0+dfsg/modules/calib3d/src/calibration.cpp, line 1396
terminate called after throwing an instance of 'cv::Exception'
  what():  /build/opencv-L2vuMj/opencv-3.2.0+dfsg/modules/calib3d/src/calibration.cpp:1396: error: (-211) The number of points in the view #2 is < 4 in function cvCalibrateCamera2Internal

But if I take several pictures of the board mostly flat in front of the lens it completes the calibration without error.

I am running it on Ubuntu 18.04 virtualbox from a Windows 10 host. Using the video mapping YUYV 640 500 20.0 YUYV 640 480 20.0 JeVois DemoArUco   

Does anyone have any idea why this happens? I'm grateful for any tips.

Answer 1

It looks like either you are not getting enough detected corners, or they are not good. Maybe the problem is that you are running the ArUco detector in the camera? You should be configuring your camera as a dumb pass-through camera, as follows:

YUYV 1280 720 10.0 YUYV 1280 720 10.0 JeVois PassThrough

or use 640x480 if that is the calibration you want to create. Just to be sure, delete all other video mappings in your videomappings.cfg on the camera, so that this one is the one that will be picked.

Please see section on "Preparing your JeVois Camera" at http://jevois.org/tutorials/UserArUcoCalib.html

You do not want the camera itself to detect the markers and then draw their outlines and then send that video with the outlines to your PC. You want the camera to just send a plain image to the PC. The PC will then detect the markers and draw the green lines and small red squares you see in the screenshot of that tutorial.