Checkerboard FOV Calculation

Imatest finds the best-fit coefficients to the radial distortion data (center-corner distances of saddle points) measured from the image using one or more of the distortion models described here, depending on user settings. It will then use these coefficients, along with the distance parameters provided by the user, to calculate the full FOV of the image. So, any change to the sampling of this data (saddle point frequency/location) can lead to a different solution and, therefore, a different FOV measurement. This is especially true with images for which only a small number of saddle points are visible. Using a high frequency checkerboard target that completely fills the camera FOV will minimize error caused by sampling.