Fig. 1. Diagram of detection device

Fig. 2. Original image of weld to be measured

Fig. 3. Flow chart of image processing based on structured light. (a) ROI; (b) Gaussian & median filtering; (c) image binarization; (d) edge extraction of line structured light; (e) central line extraction by gray centroid method; (f) final result of central line extraction

Fig. 4. Fitting image of weld surface contour

Fig. 5. Schematic of ideal scan status

Fig. 6. Schematic of spatial position deviation

Fig. 7. Schematic of rotation axis deviation. (a) Spatial diagram; (b) XZ plane; (c) XY plane

Fig. 8. 3D reconstruction of weld surface morphology. (a) Before filtering; (b) after filtering; (c) actual pipeline weld surface topography

Fig. 9. 5×5 window of weld contour data

Fig. 10. Ideal weld section

Fig. 11. Weld base plane fitting by different methods. (a) RANSAC method; (b) LS method; (c) improved method

Fig. 12. Weld edges extracted by different methods. (a) According to fitting plane; (b) from each contour line

Fig. 13. Comparison among weld surface models.(a) Idealized model;(b) minimum idealized model;(c) maximum idealized model

Fig. 14. Weld surface contour projection on different models. (a) Idealized model; (b) minimum idealized model; (c) maximum idealized model