Aircraft Video GPS

Abstract
While utilities struggle with which platform to choose and justify the dollars necessary to implement it in hardware and software, the often underrated item is the effort required to gather the vast amounts of data the new system will consume. Probably the main reason for moving to an AM/FM/GIS system in the first place is that the current records are sadly out of date and inadequate. The challenge is to find and accurate an cost effective way of updating the new system when the old records cannot be relied on. This paper describes the successful use of videographic mapping to capture right of way features.

In 1995 West Kootenay Power was well under way in developing a AM/FM/GIS Autocad based system. Also there had been a growing need for a comprehensive vegetation management program over the previous decade. Most of the utility corridors cut through forested country. The cost and liability of hazard tree removal and brushing (undercover suppression) were rising annually.

Right at the outset it was determined that we wanted as much of the brushing inventory to be captured in a single year; in effect, to get a snapshot of the corporation’s field assets at a given time. It followed from this that the only way to capture most of the some 3,000 kilometers of rural right-of-way was to use Global Positioning System (GPS) technology.

We had some experience with the capabilities of GPS, but only as used by ground surveyors. We remembered seeing a presentation in which GPS had been linked to a vertically mounted video camera in a small aircraft. The combination of(a) combining digital images and GPS together, and (b) using a light helicopter instead of a large twin-engined plane, had struck Scott as a possible alternative to the time-consuming methods of traditional ground surveying.

Testing for accuracy - how good is ‘GOOD’?
Would an airborne GPS and video system be cost competitive? And more importantly, could it match the required ground accuracies of+ 1 meter which were needed, and which were attainable using conventional ground survey methods?

Enquiries resulted in two airborne GPS contractors reaching the shortlist. The first used a helicopter which hovered over each pole, while the operator took a fix on the pole with something akin to a bomb-sight. The fix and the DGPS position were logged, and the helicopter moved on to the next pole. Given the mountainous terrain of the West Kootenay Power territory (the interior of British Columbia has valleys as low as 100m (300 ft) above sea level and peaks of over 2,500m (8,000 ft)), and the cost of this stop-start method, this option was discounted.

The alternative used a videographic technique to map the poles. Simply put, a vertically mounted video camera replaced the traditional aerial camera (with its expensive large-format film), while a sophisticated positioning system ran in the background. Later, the image data and the positional data were merged, so any video frame could be used to map the terrain.

In this process, many of the time-consuming and costly steps used in conventional airphoto (the field survey, developing & printing photos, aerial triangulation, photomosaicing and photogrammetry) were eliminated. But was it accurate enough? Could a small helicopter, bouncing through mountain turbulence, really be used to position slender power poles to sub-meter accuracy, while flying at 100 krn/hr (60 mph)?