Patent ID: 7086164

Claim:
A directional measuring device that measures a direction of a body of the directional measuring device in a three-dimensional space including an X-axis indicating magnetic north on a horizontal plane, a Y-axis orthogonal to the X-axis on the horizontal plane, and a Z-axis orthogonal to the horizontal plane, assuming that the body points towards an x-axis, comprising: an x-axis geomagnetic force detector that detects a geomagnetic force along the x-axis; an x-axis tilt angle detector that detects an x-axis tilt angle that is an angle between the horizontal plane and the x-axis; a y-axis geomagnetic force detector that detects a geomagnetic force along a y-axis that is orthogonal to the x-axis; a z-axis geomagnetic force detector that detects a geomagnetic force along a z-axis that is orthogonal to both the x-axis and the y-axis; a y-axis tilt angle detector that detector detects a y-axis tilt angle that is angle between the horizontal plane and the y-axis; a determining unit that determines the x-axis tilt angle as a rotation angle that is an angle by which the x-axis needs to be rotated around the Y-axis so as to be in the horizontal plane; a rotation angle calculator that calculates a rotation angle based on both the x-axis tilt angle and the y-axis tilt angle wherein the rotation angle is an angle by which the y-axis needs to be rotated around the X-axis so as to be in the horizontal plane when the x-axis is rotated by the x-axis by the x-axis tilt angle around the Y-axis so as to be in the horizontal plane to cause the y-axis to rotate following rotation of the x-axis, and an azimuth calculator that calculates an azimuth of the body based on the geomagnetic force and the rotation angle wherein the azimuth calculator calculates an azimuth of the body based on the geomagnetic forces detected by both the y-axis geomagnetic force detector and the z-axis geomagnetic force detector and the rotation angle calculated, and the rotation angle calculator calculates the rotation angle based on a coordinate expression for rotations three times expressed by an expression [ cos ⁢ ⁢ θ sin ⁢ ⁢ θ 0 - sin ⁢ ⁢ θ cos ⁢ ⁢ θ 0 0 0 1 ] × [ cos ⁢ ⁢ β 0 - sin ⁢ ⁢ β 0 1 0 sin ⁢ ⁢ β 0 cos ⁢ ⁢ β ] × [ 1 0 0 0 cos ⁢ ⁢ α sin ⁢ ⁢ α 0 - sin ⁢ ⁢ α cos ⁢ ⁢ α ] where α is a rotation angle around the X-axis, β is an x-axis tilt angle as a rotation angle around the Y-axis, and θ is a rotation angle around the Z-axis as an azimuth of the body.