Gap and flush generated among aircraft assembly should satisfy specific requirements

which should be precisely extracted in order to ensure the quality of assembly. Because of seam’s uneven size and noise of the data

gap and flush are difficult to extract accurately. Therefore

this paper proposes a method to extract gap and flush of threedimensional point cloud of seam based on SVM (Support Vector Machine). Firstly

mathematical model is established according to distribution characteristics of point cloud

in order to identify the feature points that need to be extracted. Secondly

measuring position points are planned and discreted according to the boundary of the digital model. Take the measured position points as the geometric center

and subpoint cloud is extracted based on PCA (Principal Component Analysis) and bounding box. Thirdly

point cloud is segmented by hyperplane which is adjusted. Then

boundary points

edge points and critical points are extracted by triangler point cloud. Finally

gap and flush are extracted according to mathematical models. The accuracy and stability of the method were verified through designed experiments. Experiments show that gap measurement mean error is less than 0.03mm as well as the flush measurement mean error is less than 0.02mm.