## 2 Benchmarking Mobile Laser Scanning Systems
### Materials
#### Benchmarked Mobile Laser Scanning Data  
Mobile laser scanning data were collected from the test field using five different systems (Tables 1 and 2). The test field was driven in both clockwise (CW) and counter-clockwise (CCW) direction at a speed of about 30-40 km/h with all of the systems. \begin{table}
\begin{tabular}{l c c} \hline
**MLS system** & **Operated by** & **Data acquisition date** \\ \hline ROAMER & Finnish Geodetic Institute & June 2009 \\ RIEGL VMX-250 & RIEGL Laser Measurement Systems GmbH & March 2010 \\ Sensei & Finnish Geodetic Institute & May 2011 \\ Streetmapper 360 & 3D Laser Mapping & June 2011 \\ Optech Lynx & TerraTec AS & June 2011 \\ \hline \end{tabular}
\end{table} 
Table 1: The tested MLS-systems. \begin{table}
\begin{tabular}{l c c c c} \hline  & **Optech Lynx** & **Sensei** & **ROAMER** & **RIEGL VMX-250** \\  & **Mobile Mapper/** & & & **and Streetmapper** \\  & **TerraTec AS** & & & **360** \\ \hline Laser scanner & Optech & Ibeo Lux & FARO Photon 80 & RIEGL VQ-250 \\ Laser wavelength & N/A & 905 nm & 785 nm & Near infrared \\ \hline Distance measurement & Time-of-flight, & Time-of-flight, & Phase-shift & Time-of-flight, no. \\ principle & max four returns & max three returns & & of returns selectable \\ Points/s (\(\times\)1000) max & 2 \(\times\) 200 & 38 & 120 & 2 \(\times\) 300 \\ Range & 200 m & 200 m & 76 m & 500 m \\ Profiles/c max & 2 \(\times\) 200 & 50 & 61 & 2 \(\times\) 100 \\ \hline Beam divergence & N/A & 1.4 \(\times\) 14 mrad & 0.16 mrad & 0.3 mrad \\ Beam size at exit & N/A & N/A & 3.3 mm & 7 mm \\ Distance measurement & 8 mm & 100 mm & 2 mm@25 m & 10 mm@150 m \\ accuracy & & & & \\ Angular resolution & N/A & 0.25\({}^{\circ}\) & 0.009\({}^{\circ}\) & 0.018\({}^{\circ}\) \\ \hline \end{tabular}
\end{table} 
Table 2: The MLS scanner specifications [32, 33, 34, 35, 36, 37]. Figure 8: ROAMER data. Figure 7: RIEGL VMX-250 data. There were still patches of snow on the ground during the data acquisition, and these resulted in voids in the data. FGl's **ROAMER** system, developed in-house [11], has been operational since the summer of 2007. Mobile mapping data from test field using this system were acquired in June 2009. At that time, the ROAMER consisted of a FARO Photon 80 terrestrial laser scanner and a NovAtel SPAN positioning system (NovAtel DL-4 plus GPS-receiver, a NovAtel GPS-702-GG antenna and a Honeywell HG1700 AG58 inertial measurement unit (IMU) with ring laser gyros). Later on, the laser scanner was updated, and currently a FARO Photon 120 terrestrial laser scanner is used. The maximum point measurement rate of the Photon 80 scanner was 120 kHz and its range was 76 m (Photon 120: 976 kHz and 153 m, respectively). The laser profiling was carried out using a scanning frequency of 48 Hz. The ROAMER has an adjustable scanning angle, and in the Espoonlahti exercise the scanner was operated for measuring profiles by having it tilted 45\({}^{\circ}\) below the horizontal; see Figure 10. The ROAMER is the only system in this comparison, which utilized a laser scanner with continuous wave laser and phase-shift-based distance measurement. The beam size of the scanner was also the smallest in the test. The direct georeferencing of the ROAMER point clouds was computed using the Waypoint Inertial Explorer(tm) GPS-IMU post-processing software. The GPS reference station data were acquired from the Finnish virtual reference station (VRS) network GPSNet.fi. After georeferencing, the dark points were deleted by filtering out points with intensity value of less than 8,000 (range 0-20,470), and isolated points were deleted by filtering out points that had less than 50 points within a 2 m radius around them. TerraScan by Terrasolid Ltd was used for the filtering. Two point clouds were analyzed for the ROAMER. In the first one, the georeferencing of the point cloud was computed using the calibration values between the instruments determined only in laboratory calibration.