# Measuring distance to the camera plane given position and orientation in ofxFaceTracker

Hi @kylemcdonald,
since you are the creator of ofxTracker I tag you directly, but anyone else is free to respond of course!

I am playing around with ofxFaceTracker and wonder how I can use (IF I can) position and orientation variables to determine where a person looks (ie where the normal vector of the face plane intersects the camera plane). I assume for simplicity that camera and projection surface can have identical normal vectors (ie lie on the same plane)

I believe orientation vector (as OSCâ€™ed in FaceOSC example) will give me the direction towards where the face is looking, and adding to the position vector will account for the head shift left - right (front - back will also be accounted for by identical triangles). Then intersection to the camera plane will be straight forward to compute.

What puzzles me is how do I find the camera plane. That is, if the origin point is the camera at (x,y,z)=(0,0,0), how is the unit vector setup? ie where does the positive z unit vector look towards compared to the camera itself.Does it point outward in front of the camera ? Can I just assume that and create 3 random points on the XY plane (say P1(-1,-1,0) , P2(1,1,0) and P0(0,0,0) ).

As you can imagine vectors are abit clouded in my mind.
If you have any nice tutorial for vectors and camera planes etc , please forward it.

thank you!

hey @synthnassizer the direction you want to look is the `example-calibrated` code that ships with ofxFaceTracker.

this shows you how to make a guess about the 3d position of the head based on a calibrated camera. it comes with a generic webcam profile that will get you pretty far. from there you can start making guesses about where in 3d someone is pointed.