Cylindrical piece measurement through laser telemetry: application to a new forest caliper

The feasibility of a new robust radius determination method of cylindrical objects is studied. The principle used is laser telemetry under structured lighting, where the object under test is illuminated by a laser plane, creating a curved line on the object, which is observed by a CCD camera. This paper presents the image processing algorithm applied to the original captured picture, and the "three-tangents method" used for the radius calculation. It shows that this method is very reliable taking into account the particular curve characteristics. We apply our method to tree measurements in forests. A pre-prototype caliper was built. Some details are given about the instrument's calibration. Finally, experimental results are presented. A general accuracy of 1% on 5 to 25 cm radius trunks was achieved for distances up to 3.5 m.