a collection of tools for solving the Perspective-n-Point (PnP) problem in compute vision

RANSAC and sevral variants are extracted from the TheiaSfM package.

PnP solvers:

1. Kneip's original P3P solver using TooN (P3p)
2. Kneip's original P3P solver using Eigen (Kneip_P3P)
3. P2P algorithm with known gravity (TODO)