Calibrating fisheye lenses above 180 degrees

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I'm in the same boat.

Ninghang said the existing model and checkerboard calibration can still be used as a good approximation if you mask off everything beyond 180° during the calibration process.

I'd like to try this method and see how it compares to a manually calibrated radial model. But before reinventing this wheel yet again... has anyone written a fisheye calibrater that allows masking off beyond 180 degrees?

I don't expect OpenCV's model to stay a close approximation past 180, but for my task I can live with that, it will also be interesting to see the divergence.

Edit: Ninghang's post was written in 2012, and OpenCV's fisheye camera model appears to have been added in 2014, so he might not have been referring to the current model. However, I was under the impression that OpenCVs fisheye calibration model is the same as this paper (2007), "known to approximate a large range of fisheye lenses" but looks to me like it will start deviating from lens behaviour beyond 180°, so I assume TAXfromDK's question is still valid for OpenCVs fisheye calibration model, and Ninghang's answer might be a solution if you don't need acurracy beyond 180°. I could be wrong - I'm still learning and haven't tried this yet, I intend to once I find/write calibration software that allows masking.