This paper proposes a displacement measuring technique for detailed noncontact mapping of the interior geometry of pipes. The technique, which is based on optical measurement using triangulation, employs a laser-beam scanner to measure radial displacement. To achieve high precision, three different algorithms for calculating the displacement from sensor output are compared in experiments. One of them, which calculates the displacement by using several direction-dependent characteristic curves, gives high accuracy. The accuracy of our experimental system is ±0.2 mm for radii between 33 and 42 mm. A mapping system using this technique with automated data-acquisition and 3D rendering of the interior is also described. Its effectiveness is illustrated by the experimental results.

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