There are several different coordinate systems used (se pictures below), and functions to convert points between them. The World coordinates are either 3D or 2D ground coordinates with the last coordinate assumed to be 0.
graph LR;
Camera -- normalize() --> Normalized
Normalized -- unnormalize() --> Camera
Normalized -- undistort() --> Undistorted
Undistorted -- distort() --> Normalized
Undistorted -- undistorted_to_ground() --> World
World -- world_to_undistorted() --> Undistorted
World -- world_to_image() --> Normalized
Normalized -- image_to_ground() --> World
