Issue link: https://geospatial.trimble.com/en/resources/i/1470951
Comparison of the Trimble MX9 and the Trimble MX50 mobile mapping systems 13 SRR, together with driving speed, is responsible for how distant scan profiles are and for the density of points per given area. Assuming equal driving speeds for both systems, the following table defines the scan line distances and the number of points per square meter at different distances: Trimble MX9 (SRR 250 Hz) Trimble MX50 (SRR 120 Hz) Profiles distance - assuming max SRR - at a certain speed 30 km/h: 3.3 cm 50 km/h: 5.6 cm 70 km/h: 7.8 cm 30 km/h: 6.9 cm 50 km/h: 11.6 cm 70 km/h: 16.2 cm Number of Pts/m² - assuming max PRR/SRR - at a certain distance - at 50 km/h 3 m: ~3850 Pts/m² 5 m: ~2320 Pts/m² 10 m: ~1160 Pts/m² 3 m: ~1920 Pts/m² 5 m: ~1160 Pts/m² 10 m: ~580 Pts/m² Profiles distance and points distribution A consequence of a slower rotation speed is the reason for not having enough points on a target and not being able to identify the exact center, for example in a registration project, as shown in the following example: Scan lines separation on targets With only a few scan lines on the targets, the scenario on the right might make it difficult to manually or semi- automatically identify the center of the checkerboard flat target. This might potentially impact the quality of the registration procedure. Laser returns The MX9 and MX50 LiDAR technology also differs with the number of returns a single laser pulse can generate. According to the laser pulse diameter, it is likely that only a part of its diameter will come across a target. This part will be reflected and will return to the detector. For single-return LiDARs, the detector triggers the Time-of-Flight measurement as soon as the first significant return comes back to the sensor. In multiple-return LiDARs, the remaining part of the beam diameter keeps traveling until it encounters other target surfaces generating other returning echo signals. The result is that the LiDAR pulse can see through vegetation or other objects, such as fences and gates, producing a potentially unlimited number of range measurements. The MX9 system is based on this technique. The MX50 lasers are based on single returns. An advantage of the MX50 lasers is that no post-processing steps are needed to remove false echoes (faster point cloud processing in the office) and smaller raw data sets are recorded in the field.