Patent ID: 8749490

Claim:
An orientation calculation apparatus for acquiring data from an input device, the input device including at least an angular rate sensor and an acceleration sensor, and calculating an orientation of the input device in a three-dimensional space having a vertical direction defined by gravity, the apparatus comprising: a processor; a memory coupled to said processor, said memory storing instructions that, when executed by said processor, control said processor to: calculate a three-dimensional orientation of the input device in accordance with angular rate data acquired from the angular rate sensor; calculate a three-dimensional acceleration vector representing an acceleration of the input device in accordance with acceleration data acquired from the acceleration sensor; and correct the calculated three-dimensional orientation by mathematically rotating the calculated three-dimensional orientation about a predetermined axis of the input device such that a projection of the acceleration vector onto a plane perpendicular to the predetermined axis is made to approach a projection of a vector representing a vertically down direction of the three-dimensional space onto the plane.