The basic camera model is a pinhole camera, though the real-world cameras that we use are far more complex models. A pinhole camera is made up of a very small slit on a plane that allows the formation of an image as depicted in the following figure:
This camera converts a point in the physical world, often termed the real world, to a pixel on an image plane. The conversion follows the transformation of the three-dimensional coordinate to two-dimensional coordinates. Here in the image plane, the coordinates are denoted as where 
, Pi is any point on an image. In the physical world, the same point is denoted by 
, where Pw is any point in the physical world with a global reference frame.
Pi(x', y') and Pw(x, y, z) can be related as, for an ideal pin hole camera:
Here, f is focal length of the camera.