An angle sensor can be used to evaluate profiles without any shape references. We regard it suitable for evaluating a large profile and consider a gyro as an angle sensor for evaluating a profile larger than 100 m with an accuracy of better than 1 mm. A gyro can evaluate profiles without restrictions in span or direction; however, angles detected by a gyro typically fluctuate unacceptably for our purpose. We demonstrate that periodical reversal measurement by flipping a gyro is effective in reducing the effect of the fluctuation. Then, we rotate the gyro for continuously realizing the reversal, where the angles of the gyro’s rotating axis against the earth’s rotating axis can be derived without being affected by the fluctuation, and can be used as an angle sensor. Here, we consider a new method using gyro signals rotating around four orthogonally aligned axes. This can improve the accuracy of the derived angles by eliminating the effects of the gyro’s scale factor as well as the fluctuations.

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