PnP algorithm & BA

PnP is a algorithm used for finding out camera poses when there are N known 3D points and their corresponding projection places.

2D-2D method, AKA etipolar method requires 8(=) pairs of points. it also has other issues.

P3P is a typical use of PnP. Note: the three points are world points rather than camera points. if these points are camera points, it will be a ICP problem.

P3P algorithm use information of 3 points, so if there are more points than 3, cant contribute to the accuracy.