Automatic Calculation Method of Three-Dimensional Side Protrusion Angle at Elastic Fixation Turning Point of Lower Waist Curve

The four-step "waist shape" can be manifested as the difference in the 3D side-protrusion angle at the elastic fixation turning point of the lower waist curve (after this, referred to as the turning point). The measurement method of this angle mainly relies on manual selection of feature points. For the problems of poor repeatability and vital subjective factors of manual measurement, propose the automatic measurement method of the 3D side-protrusion angle. The processing object is the back 3D point cloud data. The method uses mathematical features to extract 3D ridge-sulcus curve and the turning point. Then calculate the exact value of the 3D side-protrusion angle. By this method, the measurement results are as follows: The mean measurement errors on 21 targets are all less than 0.5. Repeat the measurement three times, and the result remains the same. The accuracy and stability are far superior to manual method measurement.