The quality of aircraft skin subsidence has great influence on the overall weight of aircraft

and plays an important role in maintaining the appearance of the surface. In the manufacture of modern aircraft skins

the accuracy of the aircraft skin subsidence is also raised. In this paper

a method of extracting the feature points of the skin subsidence based on T-Scan measurement is proposed in order to achieve the purpose of digital detection of the plane subsidence characteristics of the aircraft. Firstly

scanning lines are identificated from point clouds

and the 3D point cloud data is reduced to two dimensional data. Subsequently

the first and last derivatives of each point are computed by first order difference

the sag points are extracted by judging the vector angle

and the the boundary points are found by comparing the curvature of the sag points; Finally

the boundary points are projected to the line

which is fitted with data points on upper surface

projection points will be obtained as feature points of skin sag. The method directly deals with the scan line cloud data obtained by T-Scan scanning; Through the measurement and processing of actual aircraft skin

the experiment shows that the method has good practicability

the extraction precision of sag feature points is higher.