Travellers heading down through the Otira Gorge along SH73 are usually too preoccupied with the dramatic scenery or with staying safely inside their lane on the steep and winding road to think about where the boundaries of the road might lie. There are generally no fences or other features to denote exactly where the State Highway stops and Arthur’s Pass National Park begins, and the road has had several major realignments since opening in 1866. For Waka Kotahi (NZTA) who owns and maintains the State Highway network, it is vitally important to ensure that all their roading infrastructure is contained within their road corridor, and outside the strict environmental protections of the National Park.
To this end, Waka Kotahi’s agents, The Property Group Ltd (TPG) approached Fox & Associates to provide a solution to accurately map in 3D the current physical Highway corridor and associated structures in the 15km between Arthur’s Pass Village and Otira township. This solution meant that an arrangement could be reached between the various stakeholders as to where new road boundaries should be drawn.
The data needed to be accurate enough to enable the plotting of these new boundaries. It also had to be captured efficiently and safely without compromising the operation of the busy State Highway. Our solution was to provide high-accuracy imagery and a 3d model of the road corridor based upon LiDAR data captured by our Innoflight Galaxy UAV (drone). Having reviewed our proposed methodology, we received a contract to proceed with the work from TPG in January 2021.
Figure: Preparing for the UAV flight
The project presented some unique challenges which required careful and creative planning to overcome. Permission to fly the UAV over the State Highway and National Park was required, and this was gained from Waka Kotahi and the Department of Conservation early in the process.
Another major consideration was the delivery timetable as we were conscious of the alpine environment and the changing of seasons. With the onset of autumn, there was a real possibility of unfavourable weather and environmental conditions like snow cover which would blanket the land surface features we were mapping, or high winds that could make the flight unsafe.
Figure: Old-fashioned visual aid for planning meetings.
The UAV flight needed to be a mobile operation involving two vehicles, one with the pilot and one with the spotter following behind the UAV in a vehicle as the corridor was far too long and winding to keep the UAV in sight at all times. Advance reconnaissance of the survey area was also required to identify emergency landing areas and all aerial obstructions along the survey route. The latter was carried out by ‘Mobile Mapping’ - mounting our LiDAR scanner to a vehicle and driving the length of the survey area. The resultant data, while not survey accurate due to the poor GPS environment, was ideal for mapping a safe flightpath.
Finally, once the flightpath was drawn, the safety plan was drawn up to cover all contingencies and the team was fully briefed to be on the same page. On 23 March 2021, a team of four staff set off early in the morning to carry out the flights. The careful planning paid off unexpectedly on the first flight of the day as some non-forecast cloud rolled in. On the return leg of a flight, approximately 700m from the take-off point, the visibility was less than 20m.
Not only could the crew not see the UAV, but they could also barely see the road. This hazard was quickly conveyed to UAV operator, Jesse Tilling, who expertly took manual control of the UAV and turned it around to land at one of our emergency landing areas. Each person had been properly briefed and everyone performed their role perfectly to avert a potential crisis.
Contingency planning kicked in and the team deployed to another part of the site not affected by the cloud and were able to resume flying. They returned to the previously cloud-affected part of the site later in the day when the cloud had cleared.
Figure: LiDAR data showing the 440m long Otira Viaduct
Once the data was safely captured, Phil Dewar, the company’s 3D data champion set about creating the various deliverables. The dataset presented unusual challenges both in its large size and its long, thin shape. Once wrangled into a satisfactory 3D model, Phil then needed to provide information in formats that a wide variety of stakeholders of varying technical expertise could access and make use of. This included CAD files, PDF plans, and a Google Earth KML that automatically inserted the road corridor and survey accurate photos into Google Earth.
We were very proud of both of the way the team worked together to solve problems and safely achieve the project goals and of the final deliverables. The last word, however, goes to the client, Waka Kotahi’s Principal Property Manager Steve Cottrell
“The dataset provided by Fox & Associates exceeded our expectations in both quality and timeliness. It provided us with rich imagery and accurate 3D information to enable all the stakeholders to make good decisions with confidence and study the terrain in detail from a desktop location.
As Principal to the contract, it was critical to Waka Kotahi to have a safe methodology that minimised requiring people to work on a busy road in a challenging and remote alpine environment. The unique solution provided by Fox & Associates gave us that assurance.”
Figure: True colour 3D model of a section of the Highway