Camera calibration component(s)

[jonnor]

For a CNC machine at Bitraf we want to be able calculate the size of objects viewed by camera, referred to the top of material. We know the size of the working area, the camera being used and its distance from working area.
The camera is supposed to be mounted coplanar and without axis scew, but might need additional calibration/verification.

In the ideal case this should just be a scaling defined by:

• focal angle / FOV of camera
• distance to image/reference plane
• distance to (which is distance to reference - material thickness)

http://ksimek.github.io/2013/08/13/intrinsic/
http://gopro.com/support/articles/hero3-field-of-view-fov-information

Probably need to correct for distortion in the camera before applying this OP as well, but the lens-fun operations should handle that.