Solvepnp better output with P3P

[nitheeshas]

Hi,

First of all, thanks for developing this! Works like charm.

I have been messing around with this for a while now and found that P3P method of solvepnp works way better than iterative. Its very stable in profile faces, unlike ITERATIVE, which fluctuates at times, once we turn our head.

[severin-lemaignan]

Hum, interesting! I'll definitely give it a look!

[nitheeshas]

Cool. And just for the record, I used the sellion, left ear, right ear and the nose points for P3P, since P3P needs exactly 4 points as input. The reprojected nose point is almost on/below the lips, but still its steady.

Also, I have created python wrappers for this, but it looks ugly now. Once I clean up the stuff, maybe I'll create a pull request?