The last two points above can be used to design a simple calibration device as follows. The image of three squares on three different planes (not necessarily orthogonal) are sufficient to give calibration. Consider the following steps:

- For each square compute the homography that maps its corner points, to their imaged points.
- Compute the imaged circular points for the plane of that square as .
- Fit a conic through the six imaged points. Note that five points are sufficient to define a conic.
- Compute from using Cholesky decomposition.

Subhashis Banerjee 2008-01-20