Convert x, y to millimeters using depth value

[Jemaima]

I got x,y in depth space by using kinect.body_joints_to_depth_space(joints) and i got a depth value correspondent to this x,y in millimeters. So, how can i convert x,y that are pixel number of depth image to millimeters in camera space? I know only the one solution that requires a focal length of the depth camera. Is it possible to get it somehow? Or maybe there is an another way to get it?

[Ddylen]

I found what I think to be an easier method, using the kinect._mapper.MapColorFrameToCameraSpace function, which gives you a 3D position in the cameras coordinate system. I've got an example program that gets the x,y,z value of a pixel in meters in the replies to #24