The P3P and PnP Problems

The DLT solution is numerically unstable, while non-linear least squares minimization techniques are iterative methods that require a starting point for minimization that is close to the optimum (for example, the solution proposed by DLT). Currently, there are no definitive and elegant solutions to these problems, but several possible approaches exist, all of which are superior to the DLT approach. These techniques fall under the names of PnP (perspective-n-point) and P3P (perspective-3-point) in the theoretical optimal case, as only three points are needed to determine the pose of the video sensor.

Among the interesting approaches to mention are those described in (LFNP09) and in (HR11). These are relatively lengthy and complex methods, but they provide pose estimates that are very close to those obtained through iterative techniques, which still suffer from local minimum issues.