Table 1 Properties of TLS-derived point clouds for each measurement
Measurement occasion | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
Year | 2011 | 2013 | 2014 | 2015 |
Date | Jun. 23 | Dec. 5 | Dec. 4 | Nov. 27 |
Terrestrial laser scanner used | GLS-1500 | TX5 | TX5 | TX5 |
Number of scan position | 4 | 8 | 7 | 10 |
Weather conditions | Cloudy | Sunny | Rainy | Rainy to cloudy |
Internal registration error (mm) | 4.0 | 2.9 | 7.9 | 9.8 |
Horizontal GCP error (mm) | – | – | 12.1 | 11.7 |
Vertical GCP error (mm) | – | – | 23.1 | 17.3 |
Number of GCPs | – | – | 11 | 3 |
External registration errors (mm) | 6.2 | 15.7 | – | 19.8 |
Total number of measured points | 1,973,134 | 130,137,112 | 102,864,460 | 47,933,335 |
Number of points used | 1,082,832 | 52,158,136 | 69,169,926 | 30,018,333 |
Coverage area (excluding no data cells) (m2) | 1854 | 2187 | 1931 | 2122 |
Point density (pt/m2) | 583.9 | 23,845.2 | 35,814.1 | 14,143.6 |
Average point spacing (mm) | 41.4 | 6.5 | 5.3 | 8.4 |