Abstract: A method and apparatus for determining the orientation of an object relative to a coordinate system. The apparatus includes a body providing a reference for a local coordinate system. A rotatable sensor array is provided having more than one sensor and a rotational axis about which the rotatable sensor array rotates. A rotational drive system is provided for rotating the rotatable sensor array both to precise positions relative to the local coordinate system and at a precise rate relative to the local coordinate system. An angular position indicator to measure the angular position of the rotatable sensor array.

Abstract: A method and apparatus for determining the orientation of an object relative to a coordinate system. The apparatus includes a body providing a reference for a local coordinate system. A rotatable sensor array is provided having more than one sensor and a rotational axis about which the rotatable sensor array rotates. A rotational drive system is provided for rotating the rotatable sensor array both to precise positions relative to the local coordinate system and at a precise rate relative to the local coordinate system. An angular position indicator to measure the angular position of the rotatable sensor array.

Abstract: A gyroscopically-oriented survey tool, includes a housing having an axis. Three accelerometers are mounted in the housing with their axis set orthogonally. A first of the axis is aligned to the axis of the housing. A second of the axis is perpendicular to the first. A third of the axis is perpendicular to both of the first and the second. Three gyroscopes are mounted pseudo-orthogonally in the housing with their axis set at relative angles of other than 90 degrees. None of the axis of the gyroscopes are mounted parallel to the axis of the accelerometers. This configuration permits data from the accelerometers to be used to check the quality of data from the gyroscopes.