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August 29, 2013

ONTARIO MINISTRY OF TRANSPORTATION

A LiDAR point cloud of Highway 594, west of Dryden, Ont.

FEATURE | Roadbuilding

The precision of LiDAR tested on roads

Mapping and surveying Ontario roads is a critical process to ensure any changes are designed efficiently and effectively to take into account existing structures.

Ron Berg, deputy chief surveyor at the Ministry of Transportation of Ontario (MTO) geomatics office in St. Catharines, says one of the key factors in a survey is which way the road drains and where the culverts are to ensure there’s no sitting water on the surface which can lead to traction issues for users and premature surface degradation.

For the most part, he says, Ontario roads are surveyed manually and though this process is labour-intensive, it provides the accuracy to two vertical centimetres that the MTO demands.

More recently the advancement of laser technology has opened up possibilities to use mobile LiDAR — Light Detection and Ranging technology — though it’s still a long way from being an everyday option in Ontario because of cost and availability.

“There’s also a lot of planning and set-up that has to go into a project,” he said. “And it’s expensive and there aren’t a lot of suppliers of the technology.”

LiDAR, with GPS and Inertial Navigation Systems (INS), is used both in aerial surveying and mounted on a vehicle. It can be driven over roads to provide intimate and intensely accurate scans of terrain and features that in turn can generate detailed 2D CAD images.

ONTARIO MINISTRY OF TRANSPORTATION

A mobile LiDAR system mounted on an SUV. The system provides large amounts of survey data.

Known as a Mobile Terrestrial Laser Scanner (MTLS), the system tested by the MTO uses two high-frequency lasers which between them take 500,000 points of date each second — for a combined total of one million datapoints per second over a 360-degree scan.

The scan covers a circle of more than 100 metres all while travelling at regular highway speeds so the physical surveying aspect is much quicker, says Berg.

The downside is that the resulting data is just too massive for practical use, he says.

“It needs to be trimmed down because the data is just too much for people and the available software packages to work with,” he says adding the big data collected could subjected to high-level computerized analysis to extract more intelligence at some future point.

“What we need is accuracy to two centimetres vertically on the road, not so much for consistency but for slope and placement of other features so the designer who takes the information can accurately place the cuts and fills required,” he said.

The technology itself came into use about 12 years ago in Ontario and was first trialed in a mobile format in 2007 but used sporadically since.

The MTO has used MTLS in six engineering surveys in its northwestern region with contractor Tulloch Mapping Solutions.

More than 130 kilometres of highway have been recorded on Highways 17, 11, 502, 594 and 601.

The system is useful because of its accuracy, speed, safety and less disruption (no lane closures required) and amount of data it creates.

The data generates a “point cloud”3D image of geo-points which can reflect not just the road but the adjoining structures such as trees and buildings.

Most scans will pick up unidentified features which may be obscured by trees or other natural elements and will need to be flagged by the surveyor in the vehicle who is monitoring the scan on the fly. Since the data comes in so fast and the point is to keep driving, those items will need to be manually checked and reinterpreted in the field for later updates.

One of the biggest hold backs in employing the technology more often has been cost but improved mobile computing technology has impacted that hurdle.

One of the world leaders in the technology is Optex, a GTA-based company. Albert Iavarone, Optex business unit manager, said the company was started in 1974 by York University professor of physics and astronomy Allan Carswell and focused on atmospheric and particle mapping.

By the 1990s the focus shifted to airborne mapping in 1994 and in 2007 they launched the mobile version for vehicles. Over the years they’ve sold some 300 to 400 units at up to $1 million each.

The company also does all its own R&D in partnership with York University. Manufacturing is done at its Vaughan facility.

“You can get units for $150,000 or so but you don’t get the same detail at 2 cm,” he said. “It all depends on what you’re looking for.”

Clients include provincial and state authorities with responsibilities for terrain mapping and road and rail agencies looking to inventory, track and document their assets.

Iavarone agrees the big hurdle is the sheer amount of data the units generate. That’s a challenge Optex is working with now because the market is highly competitive.

“The LiDAR market is growing by 20 per cent a year,” he said. “There’s strong demand from many segments.”

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