Attitude sensing apparatus for determining the attitude of a mobile unit

An attitude sensing apparatus for determining the attitude of a mobile unit by successively performing a process of estimating an alignment angle between an antenna coordinate system of a GPS attitude sensing system which determines the attitude of the mobile unit in the antenna coordinate system and an IMU coordinate system of an IMU attitude sensing system which determines the attitude of the mobile unit in the IMU coordinate system and thereby integrating the attitudes of the mobile unit determined in the individual coordinate systems, said attitude sensing apparatus comprising:

• an alignment angle estimator for successively estimating an alignment angle to be used in a succeeding calculation process based on the difference between inertia data calculated from observations by said GPS attitude sensing system and inertia data observed by said IMU attitude sensing system;
• and
• an alignment angle adder for generating an updated alignment angle by cumulatively adding the successively estimated alignment angle and thereby updating the estimated alignment angle in sequence and for outputting the updated alignment angle to said alignment angle estimator;
• wherein the estimated alignment angle is successively fed back for use in the alignment angle estimation process.