“A perfect device to scan more than one track at the same time was the laser scanner”
Central Amsterdam, alongside Schiphol Airport, is connected through a 17-kilometer passenger train route, Europe’s busiest airport by passenger traffic. Every year, millions of passengers use Schiphol Tunnel, and any disruption affects travelers going and coming from the airport. Moreover, since trains travel to other parts of Belgium, France, and the Netherlands, the integrated train network prioritizes reliability and safety.
How 3D Laser Scanning Services are Being Used
An agency responsible for the maintenance and expansion of the national railway of Dutch is ProRail which is government-owned. ProRail commissioned a geodetic engineering firm in Dutch in 2020 to survey Schiphol Tunnel to build a detailed 3D model using digital 3D laser scanning services, which can be used in planning repairs with upgrades.
A very realistic model was necessary to ensure the alignment of new tracks and the appropriate movement of the fast-paced passenger trains. GeoNext had to use top-notch tools and adhere to stringent workflow protocols to capture data with a precision of 7 mm or greater.
The deficiency of GNSS underground, the prerequisite of 7-mm, and the need to carry out tasks surrounding the train timetables all made surveying the tunnel a unique task. Furthermore, since accessibility was restricted to the Schiphol Tunnel, scheduling maintenance days for quick scanning using 3D scanning services was essential.
GeoNext is surveying rails and laser scanning, GNSS base, total stations, Trimble TX8, laser scanners, and rover systems. For quick and precise surveying, 3D laser scanning is ideal. The laser collects 1 million points per second and delivers high point density, which is significant merit in dealing with tight deadlines. In addition, in a difficult setting like a tunnel, the sturdy design of surveying instruments provides reliable operations.
“A perfect device to scan more than one track at the same time was the laser scanner,” said a project manager at GeoNext, Daisy Sparla.
GeoNext employed immediate risk exits to install GNSS stations outside with GNSS receivers R10 and R12 to compensate for the tunnel’s absence of GNSS. They aligned the outdoor GNSS locations with objectives inside the tunnels using the Dutch height system NAP. Finally, GeoNext used total stations with prisms to determine the coordinates of these targets inside the tunnel.
With the entire station, the team of GeoNext acquired roughly 750 scans, scanning every 20 m and overlapping 5 to 10m. GeoNext achieved the required scan of 7-mm accuracy thanks to setting up a close scan spacing and overlap amid successive scans. As a result, the two 6.5-km dual-track tubes in just four weekends were surveyed by the team.
GeoNext used software to process the digital 3D laser scanning services data known as Realworks once it was completed. The feature to auto-extract in the software aids in the identification of targets and the matching of scans. The point cloud was given in RD-NAP format, and Bentley MicroStation Connect was used to generate the complete digital 3D scanning model of tracks and objects (coordinate system Dutch). The team surveying was able to meet up with the tight deadline due to the digital 3D scanner’s speed.