Measuring distance from objects to origin (Curling sport)

Currently working on a group project, where our goal is to measure the distance to the centre of the house in curling, from all curling stones in the house.
My plan is to have a stationary camera directly above the centre of the house, but i don’t know how to define this centre as a coord (x,y) = (0,0), and measure distances from this origin to the stones centre.
The stones are of different color, and they need to be differentiated from each other.
I want to create a list of the object, identified by red and blue color, with the distance from the origin. Help is much appreciated!

the usual way is to use a calibration pattern and place it precisely in relation to the point you want to designate, measure the pattern’s position, and use that information.

you can print an AR marker or a checkerboard pattern. you’d define some kind of “crosshairs”, a precisely defined distance to the side of that marker/pattern, so the pattern stays whole (no holes in the pattern itself).

you’re gonna want to calibrate the camera itself (camera matrix and lens distortion coefficients) and then also calibrate the camera’s position to the ground plane. for that you use markers/patterns, place them on the ground in precisely known locations (a big rectangle of right angles and measured edge lengths).

given those four corner points, you can calculate a homography that maps the view of the ground (which may be at a slight angle) into a rectified version of the ground (and the other way around).