Locating the origin of the reference system

Hello all,

I am trying to locate the origin of the reference system in a D435i camera, the point from which the depth and the x-y coordinates of every point in a point cloud is measured.

The "Intel® RealSense™ Product Family D400 Series Datasheet" document explains that the origin x-y coordinates are obtainable from the following drawing:

The same document explains that z-coordinate of the origin is instead located at a depth of 4.2mm from the surface of the front glass, as shown in the following image:

Downloading the official CAD model of the sensor, I have discovered that the surface of the glass is 0.65mm offset, compared to the front side of the aluminum case. Here is a screenshot of the CAD as it is visualized in my CAD environment:

Therefore, I am wondering if the z-coordinate is to be located at -4.2mm from the origin of the CAD model or -4.2mm from the surface of the glass (resulting in -4.85mm from the origin of the CAD).

I am checking with you, since I need an accurate registration of the points in the point clouds relatively to the reference system of a robot, which manipulates the D435i camera.

Moreover, I am wondering if anyone of you knows how to calibrate the real position of the reference system. Obtaining the real x-y-z coordinates of the optical origin of the camera (e.g. relatively to the centre of the back surface of the camera), would allow me to not rely on inaccurate CAD positioning of the origin.

If anyone can help, it would be very useful.

Kind regards,

Carmelo