Intrinsic Calib
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The intrinsic parameter matrix, K, is a function of the camera lens and chip and is not a function of the specific installation, i.e. the camera location and viewing angles. As a consequence, the parameters in K are found during a lens calibration prior to camera installation. We use the excellent Caltech calibration package (http://www.vision.caltech.edu/bouguetj/calib_doc/). Lens calibration is described here.
The form of K is
(3)
Here fU and fV are the focal lengths in the U and V directions, expressed in pixels, U0 and V0 are the coordinates of the principal point (geometric image center), and s is the image skewness (cosine of the angle between the U and V axes) and is assumed to be 0.0. K has 5 degrees of freedom (DOF) with values returned during the calibration process. Because the number of degrees of freedom will be important to the following discussions, we will use numbers rather than words to enumerate them.
Note that the lens calibration process also computes estimates of lens distortion parameters, used to convert between image locations from the camera and those that would have been returned from a perfect camera with no lens distortion. Some cameras such as those with fish eye lenses exhibit severe barrel distortion, for example a highly curved horizon that must be corrected for. But even fairly accurate lenses requires calibration and distortion removal. This process is always used but is not described further in the discussion below (see the Caltech toolbox).