Table 3.

Tunnel point cloud data.

ID	Number of Points	Number of Pre-Processed Points ${}^{\mathit{a}}$	Length (mm) ${}^{\mathit{b}}$	Observation Position (m) ${}^{\mathit{c}}$	${\mathit{W}}_{\mathit{a}}$ (mm)	B (mm)
1	3,741,570	538,935	28,247	75.0	1000	200
2	3,858,638	555,716	27,305	77.5	1000	200
3	1,616,947	232,991	17,720	82.4	1000	200
4	1,439,603	207,476	18,289	87.8	1000	200
5	1,546,882	222,809	17,786	95.6	1000	200
6	1,600,717	230,533	19,756	100.5	1000	200
7	2,240,123	322,657	16,660	105.9	1000	200
8	1,709,192	246,209	20,360	109.8	1000	200
9	2,265,829	326,387	17,913	121.3	1000	200

${}^{\mathrm{a}}$ The voxel size is 26 mm. ${}^{\mathrm{b}}$ The length of the group point cloud along the X-axis. ${}^{\mathrm{c}}$ The observation position relative to the exit of the tunnel.