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I noticed from this page: http://docs.opencv.org/trunk/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html#id7

That the radial distortion portion of the lens model has changed from previous version such as this http://opencv.willowgarage.com/documentation/camera_calibration_and_3d_reconstruction.html

Basically the old model was u = d ( 1 + k_1d^2 + k_2d^4 + ...) where "u" is the undistorted radius and "d" is the distorted radius. That appears to have changed to

u = d ( 1 + k_1d^2 + k_2d^4 + ...) / ( 1 + q_1d^2 + q_2d^4 + ...)

(note in the documentation page q_1 etc are k_4+, and u,d are separated into x", x', y" and y' but hopefully you get the idea.

The older representation I have seen over and over for many years but this new representation is a surprise to me. Is there any references or comments on when this newer model is useful (like more fisheye lenses for example)??

Thanks Don