Fig. 1. Progressive filtering algorithm implementation process

Fig. 2. Contour generation flow chart

Fig. 3. Aerial photography of the survey area

Fig. 4. Contour to determine the shape of the stadium

Fig. 5. Point cloud contour filling distribution in the building area

Fig. 6. LiDAR point cloud distribution in the building area

Fig. 7. Tilt angle to determine the same height difference

Fig. 8. Isometric line-morphological filtering algorithm flow chart

Fig. 9. Contour determination window threshold

Fig. 10. Distribution of point cloud

Fig. 11. Samp23 survey area before and after filtering. (a) Before filtering; (b) after filtering

Fig. 12. Filtering accuracy of different height difference thresholds (window threshold is 30 m)

Fig. 13. Filtering accuracy of different window thresholds (height difference threshold is 20 m)

Fig. 14. Filtering results of different algorithms in the FSite8_red2 survey area. (a) TIN algorithm; (b) morphology algorithm