A method of estimating an orientation of a body is provided. The method includes determining a reference point based on a first region of a body, calculating a translation matrix of a world coordinate system based on the reference point; determining a first vector based on the reference point and a second region of the body, calculating a first rotation matrix rotated by an angle α about a first rotation vector, which is perpendicular to the first vector and a Z-axis of the world coordinate system, as a first rotation axis, determining a second vector based on the first vector and a third region of the body, calculating a second rotation matrix rotated by an angle β about the Z-axis of the world coordinate system as a second rotation axis, and calculating a transformation matrix based on the translation matrix, the first rotation matrix, and the second rotation matrix.