I am new in robotics and I am working on a project where I need to pass the coordinates from the camera to the robot.
So the robot is just an arm, it is then stable in a fixed position. I do not even need the 'z' axis because the board or the table where everything is going on have always the same 'z' coordinates.
The webcam as well is always in a fixed position, it is not part of the robot and it does not move.
The problem I am having is in the conversion from 2D camera coordinates to a 3D robotic arm coordinates (2D is enough because as stated before the 'z' axis is not needed as is always in a fixed position).
I'd like to know from you guys, which one is the best approach to face this kind of problems so I can start to research.
I've found lot of information on the web but I am getting a lot of confusion, I would really appreciate if someone could address me to the right way. 
I don't know if this information are useful but I am using OpenCV3.2 with Python
Thank you in advance
Define your 2D coordinate on the board, create a mapping from the image coordinate (2D) to the 2D board, and also create a mapping from the board to robot coordinate (3D). Usually, robot controller has a function to define your own coordinate (the board).
Translation from Camera Coordinates System to Robotic-Arm Coordinates System