On the use of the inclinometers in the PnP problem

This paper deals with the problem of estimating the relative pose between a camera and an object. It is assumed that both the camera and the object are equipped with an Inertial Measurement Unit (IMU) which measures their inclinations with respect to the gravity vector. Moreover, it is assumed that the object contains a feature of n ≥ 2 points, the position of which in the object reference frame is known a priori. The resulting pose estimation problem can be seen as a PnP problem with inclination information. Early results of the authors on the subject showed that in this case the P2P problem always gives 2 solutions, except for a few singular configurations where the number of solution is infinite. Moreover, to avoid singular configurations and to resolve ambiguities a very simple solution for the P3P problem, based on the idea of re-projection, was proposed. In this paper, it will be shown that, thanks to a simple test based on geometrical considerations, very often one of two solutions of the P2P problem can be discarded. Moreover to solve the remaining ambiguities and to ameliorate the pose estimation, a novel and more robust algorithm for the general PnP problem will be proposed. The results will be validated through numerical and experimental tests.