More clarity needed on 'camera position' - what location on what camera component do we mean?

[JGoldstone]

The documentation (see 'Projection, Camera Coordinate System and Screen Window' here) says

We assume that a camera is located at the origin, O, of a 3D camera coordinate system

...but we never get specific about just what part of the camera is at the origin. Is it the image plane? Is it the entrance pupil? Is it the 'pinhole' of a pinhole camera model?

Also note that our entire definition of focus distance is this:

//
// focus -- the camera's focus distance, in meters
//

IMF_STD_ATTRIBUTE_DEF (focus, Focus, float)

and we never state from what part of the camera that focus distance is measured. SMPTE's camdkit measures focus distance from the image plane as do some camera vendors (cf. SMPTE RDD 55, 'Material Exchange Format — Carriage of ARRI Camera System Metadata').

Thus the clarification process will entail not just documentation cleanup in the browsable documentation but documentation cleanup in the comments of definitions in ImfStandardAttribute.h as well.