OpenCV Fisheye Calibration FOV 220

kakeru-516 · September 18, 2021, 11:08am

Nice to meet you. I’m trying to calibrate an super wide angle(FOV220) fisheye lens.
This lens is an Entaniya lens. However, according to the OpenCV documentation, this lens cannot be calibrated to more than 180degree. If anyone knows anything about this, please help me.

crackwitz · September 18, 2021, 12:09pm

OpenCV currently does not support fisheye cameras with more than 180 degrees.

there seems to be effort to implement APIs for your situation.

I see these issues and pull requests:

Add support for super-fisheye lenses · Issue #15923 · opencv/opencv · GitHub
cv::fisheye::projectPoints ignores 180 degree FOV · Issue #19433 · opencv/opencv · GitHub
WIP Add Super Fisheye Lens Support by danielenricocahall · Pull Request #19904 · opencv/opencv · GitHub
Fisheye model extended with additional plane to support FOV > 90 in projectPoints by dmitry42nd · Pull Request #16926 · opencv/opencv · GitHub
Support for super-fisheye lenses (i.e., opening angles above 180 degr… by vpisarev · Pull Request #6801 · opencv/opencv · GitHub

I notice that the math notation on the fisheye documentation page is awful. someone should file an issue on github and maybe make a patch

github.com

opencv/opencv/blob/15ba3e123f1efa5444951b638ce6bd200054820e/modules/calib3d/include/opencv2/calib3d.hpp#L402-L434

    
      
          @{
            @defgroup calib3d_fisheye Fisheye camera model
          
          
  Definitions: Let P be a point in 3D of coordinates X in the world reference frame (stored in the
            matrix X) The coordinate vector of P in the camera reference frame is:
          
          
  \f[Xc = R X + T\f]
          
          
  where R is the rotation matrix corresponding to the rotation vector om: R = rodrigues(om); call x, y
            and z the 3 coordinates of Xc:
          
          
  \f[x = Xc_1 \\ y = Xc_2 \\ z = Xc_3\f]
          
          
  The pinhole projection coordinates of P is [a; b] where
          
          
  \f[a = x / z \ and \ b = y / z \\ r^2 = a^2 + b^2 \\ \theta = atan(r)\f]
          
          
  Fisheye distortion:
          
          
  \f[\theta_d = \theta (1 + k_1 \theta^2 + k_2 \theta^4 + k_3 \theta^6 + k_4 \theta^8)\f]

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kakeru-516 · September 18, 2021, 12:32pm

Thanks for responding.
So does this mean that it is currently not possible to calibrate fisheye lenses above 180degree?

crackwitz · September 18, 2021, 12:49pm

I think that is correct.

what do you need to do with the image data? perhaps you can implement some calibration yourself.

kakeru-516 · September 18, 2021, 1:09pm

I want to calibrate it to find the angle between the lens and the target object.

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OpenCV Fisheye Calibration FOV 220

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