Fig. 1. Schematic diagram of variable resolution scanning. (a) Large-field low resolution scanning; (b) high resolution scanning of local area

Fig. 2. Flow chart of variable resolution scanning

Fig. 3. Multi echo region judgment. (a) Target region; (b) (c) schematic diagrams of scanning echo signal

Fig. 4. Multi echo region demarcation. (a) Target region; (b) region echo

Fig. 5. Construction of experimental system. (a) Composition of the experimental system; (b) system shooting scenes; (c) target to be measured

Fig. 6. Low resolution acquisition and multiple echoes of full field of view scene. (a) depth image with 5 pixel × 5 pixel; (b) multi-echo region

Fig. 7. Target region image and echo. (a) Reconstructed depth image of the target area with 6 pixel × 4 pixel; (b) echoes of each sub-region in the target region scanning

Fig. 8. Super resolution depth map of the target region with 120 pixel × 80 pixel. (a) Distance image; (b) three-dimensional (3D) image

Fig. 9. Target region. (a) Measured target area; (b) relative position of the target

Fig. 10. Experimental results. (a) High resolution scanning reconstruction of 3D images; (b) low resolution scanning reconstruction of 3D images; (c) high resolution scanning reconstruction depth map with 18 pixel × 18 pixel; (d) high resolution scanning reconstruction depth map with 9 pixel × 9 pixel; (e) depth map of the target area in Fig.10 (c); (f) 4 times the upper sampling depth map of the target area in Fig.10 (d); (g) depth map of the target region super-resolution reconstruction in Fig.10 (d)

Fig. 11. Distance error distribution of reconstructed depth image in target region. (a) Low resolution reconstruction; (b) high resolution reconstruction

Table 1. Scanning parameters in the experiment