End of the line for Network Rail's surveyors as GIS techniques take over

3D modelling is rapidly replacing track-side engineers in tasks such as monitoring, early stage site surveying and vegetation control

Network Rail, owner and operator of Britain's rail infrastructure, is currently undertaking a £325m transformation programme called ORBIS (Offering Rail Better Information Services) which aims to improve the ways that information about the rail operator's assets is gathered and stored.

"If I were to summarise the programme in one sentence I would say 'do the right things in the right place at the right time'," says Marco Sala, senior geographical information specialist at Network Rail.

As part of ORBIS, last year helicopters flew the length of the entire network, 250 metres up, to undertake a comprehensive aerial survey of Network Rail's assets. On board each of these helicopters were three cameras equipped with LiDAR (Light Detection And Ranging) sensors.

"You build up 3D images with LiDAR, which is basically light-based radar," explains Charles Kennelly, CTO at Esri UK, whose geographical information systems (GIS) mapping software, ArcGIS, Network Rail uses to interpret the resulting "point cloud" to create models of the environment that are accurate to within just a few millimetres.

Kennelly continues: "By simply scanning the terrain you build up a point cloud. If you shine a laser at something it bounces back a certain distance, and you have a dot that tells you what it bounced off and what colour that dot was and you use that to construct models of what's there."

So once you have created your high-res 3D models from these point clouds using GIS software what can you do with them? According to Sala you can accomplish a lot of tasks from the desktop that have traditionally been done manually.

"If you have LiDAR data you can build something called a digital terrain model, which is basically a geospatial representation of the ground without any of the above ground assets," he says.

"That one is used for many applications ... Because the resolution is so high it can be used for making detailed assessments of the flood risks, et cetera, before you build a new platform for example."

Such elevation checks have traditionally been done by railway engineers and structural surveyors taking measurements on the ground. There are other tasks that workers on the ground will find themselves doing much less of in the future too, including maintenance.

"One good example is we can survey level crossings. The level crossing wears away so there's a need to monitor the angle. We can now do that with the terrain model without sending anybody out so that saves a lot of fieldwork," Sala says.

With prior knowledge of the soil type, the stability of earthworks can be assessed remotely by monitoring the slope of an embankment.

"What we look for is geometric information, how steep a slope the embankment has and digital terrain modelling gives you this information."

There are obvious safety and efficiency gains to be had, Sala explains.

"At the moment people are actually crawling up and down those earthworks and measuring them but now we can do those measurements as a desktop exercise using GIS. So you're not shutting down the railway, you're not putting anyone in danger and you're not spending money sending people out there."

For construction projects, digital terrain modelling is currently accurate enough only for the early stages and, for now at least, detailed site surveys by fieldworkers are still necessary.

"We capture the data to an accuracy of 25mm which is not very good if you look at the life-cycle of the project, but it is good enough for the early stages of an infrastructure project, for example. If you need to do detailed design you still need to get out a measure. But for the first phases of a project this data can be used," says Sala.

For how long traditional surveyors will be needed on railway construction sites Sala declined to guess, but many routine maintenance and lower-level surveying jobs will surely be displaced by technology sooner rather than later, not least because once the baseline models have been built up, spotting changes in the terrain will become much easier to achieve remotely.

"This is just the beginning," Sala explains. "We are building the base layer and then with future surveys we can prepare the various datasets captured at different times to derive the delta, so we can see if there has been any movement of the ground."

Vegetation control, finding and removing trees that might pose a danger, has been a key driver for the GIS-based project, Sala says. This is another job that has typically been very labour intensive.

"We apply a risk model that was developed two years ago in Scotland to highlight the individual trees that present the highest risk to the railway. That is massive because at the moment you have off track engineers just walking the line, up and down. This information allows for more targeted intervention. They simply go to where the problem is."

Combining the GIS with mapping data also allows Network Rail's engineers to quickly work out who owns the land on which a problem tree is growing. Because boundaries are not always clearly marked, this has been a thorny problem in the past, and the cause of expensive delays.

"We can't go and chop down their trees. But now we have the information in the GIS together with an ordnance survey address layer we can easily and quickly communicate information and contact the owner of the land. This is another way the GIS comes in handy," says Sala.

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