Distortion Models
To take the bending effects of lenses, especially those with a high field of view (FOV), most accurately into account, different distortion models have been introduced over the years. uvc ros driver supports two of those models:
- the radtan model
- the equidistant model
Both models are based on the following intrinsic parameters derived from the calibration:
- focal length
- principal point
- distortion coefficients
The following models will describe a method of deduction of a pixel's position in the incoming distorted image from the given parameters with respect to the specific model characteristics.
The radtan model is primarily targeted towards lenses with a low FOV up to 100° as the model itself treats the incident rays as unbent and corrects minor distortions with the obtained distortion coefficients both radially (parameters kc1, kc2) and tangentially (parameters kc3, kc4).
The equidistant model reflects the nature of physical lenses better and can thus be applied for fish-eye lenses up to 170°. Like other commonly used models the equidistant model's distortion depends on the incidence angle of incoming rays. For the following calculations, the average focal length of the focal lengths in x and y direction will be used. Due to the fact that most camera sensors use square pixels, they are usually very similar.
Additionally the distortion coefficients compensate the model's insufficiencies and lens imperfections. In contrast to the radtan model there are no tangential corrections.