Using optical survey software to identify precise locations on railway lines.
Over approximately eight weeks in the winter of 2013/2014 throughout the United Kingdom, Network Rail’s infrastructure suffered extensive damage. Embankments collapsed into cuttings, overhead lines were severely damaged and in Dawlish, part of the coastal railway retaining wall collapsed into the sea. There was a massive amount of collateral damage to the national rail network throughout the UK notably across the flooded Somerset Levels. Conventional survey methods with survey teams driving to the affected areas and conducting visual inspections were overstretched. Something faster was required.
- We were given helicopters and gyro-stabilised joystick-driven camera housings with Canon 1D DSLR cameras using 85, 150 and 400mm lenses.
- We integrated nationwide RTK GNSS (<10cm 3DRMS) positions, Inertial Navigation for the camera and image grabbing software called OPTOnav for use in the “cab”.
- Using these tools, we developed practical techniques to align imagery and position targets to within 35cm (3DRMS) at a range of 500m in real-time at speeds of up to 65 knots. This identified failed insulators and frayed powerlines on overhead pylons. OPTOnav located landslips, floods, treefalls and damaged infrastructure over a 120 mile stretch in both directions within five hours. We could also change equipment onto different helicopters each day and still achieve precision. This fast inspection would previously have required either an inspection train or if the line was blocked survey teams on the ground. The time is hard for us to estimate but it could be several weeks for the same number of people that we had in the aircraft.
Requirement
- We were asked to provide a solution that could fit to three Twin Squirrel helicopters on a day-by-day basis. They would typically fly at 65 knots and locate all infrastructure damage on a high-res camera image by cursor while computing the damage location to <50cm 3DRMS at a range of 500m from the helo.
- We also had to enable aerial surveyors and infrastructure engineers straightforward review and edit of all video and inspection reports in-flight and retrospectively. There were massive issues such as variable flex in the airframe (>2 degrees), vibration, data flow, aircraft power, projectile hail, snow and rain, position variations of equipment on the aircraft from flight-to-flight and occasionally malfunctioning equipment. The software programmers and hardware engineers learned how to counter all these issues systematically and precisely within the system.
- At 65knots the whole 50cm error budget could be lost in a just over a hundredth of a second if we didn’t precisely time synch, GNSS, INS, turret and camera mid-exposure pulse. We delivered on-time, tested the equipment in flight, instructed the aircrew and finally supported them during the bedding-down period. Our engineers time-synched all data from the devices with microsecond accuracy. This ensured a high level of precision in positioning.
- To deliver in August having been given a contract at the end of April.
Solution
- Our engineers used airborne turret mounts previously used for filming blockbusters such as StarWars from GSS in California.
- We integrated inertial navigation, satellite navigation and satellite communications to deliver RTK quality GNSS corrections in real-time produced the final solution. That was 2014.
- We developed techniques to rescue damaged data and make it usable. It was intensely challenging but also satisfying as a project experience for the electronics and software development team.
- We measured aircraft heading, roll, pitch and yaw to ~0.02 deg RMS consequently a target at 500m had a position computed to 35cm (RMS). This meant combined angular error had to be <0.02deg (95%)
- Our project engineers took it in turns to flight-test the system with the Network Rail Inspection Team.
- We redeveloped water-resistant electronics housings into IP67 housings. No water ever got into the INS housing regardless of weather and being positioned ahead of the helo cab.
- The same system has remained in constant use for about 250+ flying days/year across two or three helicopters. This year see its ninth year of service.
Previous experience of aircraft high-speed dynamics includes our involvement in a TV project to instrument the World Champion pilot’s aircraft for the Red Bull’s World Series Air Races. Using similar GNSS and near-identical INS we achieved <10cm (3DRMS) at up to 10G. This data was used to project a time-synched 3D trajectory onto live TV to compare each pilot’s performance.
