Mobile mapping at high speed

The Midland Mainline (MML) is an integral portion of the United Kingdom’s rail network. With 639 kilometres of track, 16 tunnels and 35 stations, the MML has been serving the UK since 1870.

Periodic maintenance and upgrades are needed to keep the rail line functioning at optimal speed. As part of the MML Enhancement project, significant alterations were planned for the Market Harborough Station in Leicestershire, England to remove a major kink in the through alignment. The project required 8 km of the mainline surveying, consisting of high accuracy track alignment, structure gauging, drainage tracing and topographic cess detail.

Severn Partnership, a surveying firm of Chartered Geomatics Surveyors based in Shrewsbury, UK, was selected to provide the high accuracy surveying needed.

Survey grade results from mobile mapping

Severn Partnership has been involved in the MML upgrade projects since 2010. This programme of improvements to the line is the most extensive since it was completed in 1870, with Severn Partnership delivering more than 161 km of permanent survey control and subsequent permanent way (P-Way) track survey. More than 70 bridge structures and three mainline train stations were added as part of the Electrification Programme. Severn Partnership installed all surveys relating back to the original snakegrid control.

Combined with its knowledge and expertise in the rail industry, Severn Partnership, needed a safe and cost effective method of capturing topographical line side details of the 8 km site at Market Harborough. The firm used its Leica Pegasus:Two survey grade, mobile mapping system to reduce track access requirements and to capture topographical detail.

Mobile mapping combines laser scanning technology with GNSS and motion sensors into a single unit that is easily mounted onto any vehicle. In a rail environment, Leica Geosystems considers mandatory the use of the second GNSS antenna. The Leica Pegasus:Two system requires GNSS coverage at all times, ensuring an accurate dynamic performance of the IMU by continuously calibrating it to zero drift.

Mounted on a motorised personnel carrier, it captured a 3D laser scan point cloud and imagery. This was done on a rail mounted vehicle, at 16 km/hour for the length of the site in a single 3 hour shift. The resulting data could then be digitised at the office without the time and safety pressures inherent with working on the railway network.

To maintain high accuracy, the point cloud was linked to the site grid using the newly surveyed track alignment. The rails in the scan were automatically matched to the traditionally surveyed rail strings, resulting in sub-10 mm accuracy relative to the track alignment.

“Working with the Leica Pegasus:Two on the Midland Mainline Speed Enhancement project saved us significant time and cost,” said Rollo Rigby, Severn Partnership associate director.

Safer with mobile mapping

The Pegasus:Two offered survey grade accuracy and high resolution images required for the project specification. Its versatility in being mounted on to any kind of vehicle enabled it to be mounted to a rail enabled vehicle as well as a road vehicle to capture all on and off track data. Using mobile mapping and the Pegasus:Two meant that the data was captured in one shift on one weekend as opposed to multiple weekends if more traditional methods were used.

Fewer rail teams were on the ground working in a potentially dangerous environment reducing risk to personnel. All detail was captured quickly and efficiently including cess detail, ballast profile, structures and vegetation, without the need for site visits. Site imagery was also shared with the project team in a ‘street view’ style potentially reducing the need for further site visits.

“In this project, with mobile mapping, we were able to reduce man hours on the track as well as improve the overall safety for the rail team,” concluded Rigby.