I'm using solvePnP (with EPNP) to find 3D face orientation. But I have different results : Sometimes it's good, sometimes it's almost good but with 180° rotation /Zaxis and/or -90° rotation /Yaxis.
The errors are constant, but I don't find any correlation between inputs and error.
For information I use IMM face database + landmarks and 3D model from http://aifi.isr.uc.pt/Downloads/OpenGL/ normalized between [-1 1] with 5 points for pose guess to avoid too much co-planar estimation, and noise impact.
Someone already had this kind of problem ?