Article originally published on Spatial Source.com.au
By integrating survey data acquired from a variety of instruments, a Queensland firm has provided its client with high precision design criteria in a format the client can literally see, not just imagine.
Cotton and grain growers on Queensland’s Darling Downs rely on the rail line through Toowoomba and the Lockyer Valley to transport their produce to the Port of Brisbane.
Many tunnels on the line are heritage listed, having been built in the 1860s. With produce containers increasing in size, the old rail tunnels will soon be too small. Worse still, along each tunnel the width varies, roof heights are inconsistent, and walls and roofs have irregular projections.
South East Queensland based survey and planning firm Bennett + Bennett were engaged for a high precision survey of eleven tunnels up to 540m long, with a view to the tunnels being preserved but having their floors lowered and the track realigned – to provide the necessary freight clearance.
The rail line is busy every day with passengers, coal freight and agricultural products. To miminise disruptions, Bennett + Bennett utilised and integrated laser scanning and conventional survey; they formed an eight-person specialist survey team to capture all the necessary data, while only having full access to the rail corridor during one 48-hour track closure.
Bennett + Bennett exclusively uses Leica laser scanning equipment, and sources its equipment and support services from C.R.Kennedy – the national distributor for Leica Geosystems products in Australia.
The team used total stations to pick up ground surface topography, underground services, Queensland Rail’s reference markers and other features outside the scope of 3D laser scanning.
During the 48-hour track closure, various engineers, project managers and geotechnical and heritage consultants were also working in the tunnels, so flexibility was essential when setting up for point cloud data acquisition. For this reason, mobile laser scanning from a rail mounted trolley would have been impractical. Scanning the irregular terrain outside the tunnels would have been difficult too.
Instead, the survey team used Leica P20 and P40 ScanStations to acquire the point cloud data from 250 locations, concentrating on features such as the tunnel approaches, portals and interiors and the tracks themselves. C.R.Kennedy made a P40 ScanStation available for hire to the survey team at short notice. It proved so efficient that the team ended up buying it. Data was recorded on a grid smaller than 5mm, and more than 100GB of data was acquired for each tunnel.
To provide the client with a realistic colour visualisation of the data, Bennett + Bennett also took 360 degree panoramic photographs at each control point. This required artificial lighting inside the tunnels. The project area was also captured on video for quality assurance purposes.
The raw scan data and panoramic images were then imported into Leica Cyclone 9.1 software for processing and registration to survey control. Features were then extracted from the point clouds to form a detail survey, while precision 3D digital meshes were created using the 3DReshaper program. Rail track designers will later use a digital model of the new trains to ensure there’s sufficient clearance to the features defined by the mesh.
TruView files were also generated from Cyclone 9.1 and were uploaded to Leica’s TruView Global software. This has allowed the project to come to life in dimensionally correct photorealistic digital reality and has enabled users to view the project, pan, zoom, measure and markup.
Data acquisition was completed within the 48-hour track closure; no further site visits were required, and Bennett + Bennett delivered their client’s high quality design requirements within two weeks of completing the field work.
A sample of the digital reality of the tunnels can be seen in a 2 minute video – HxGN Live 2017 presentation.