formula_17 are the extrinsic parameters which denote the coordinate system transformations from 3D world coordinates to 3D camera coordinates. Equivalently, the extrinsic parameters define the position of the camera center and the camera's heading in world coordinates. formula_18 is the position of the origin of the world coordinate system expressed in coordinates of the camera-centered coordinate system. formula_18 is often mistakenly considered the position of the camera. The position, formula_20, of the camera expressed in world coordinates is formula_21 (since formula_22 is a rotation matrix).