Terralink starts biggest ever aerial photography task

3 March 2004

Coverage Area

A consortium of South Island local authorities brought together by land information, mapping and data integration company, Terralink International, is taking part in New Zealand's largest and most ambitious aerial photography project.

Councils involved include Waimakariri, Ashburton, Timaru, Waimate, Waitaki, McKenzie, Environment Canterbury, and Department of Conservation, although the coverage will also take in districts of the Kaikoura, Hurunui, Selwyn and Banks Peninsula councils.

The massive undertaking involves two specially equipped planes covering more than 42,000 square kilometres from Kaikoura to the McKenzie Basin.

Approximately 2,500 photos will be taken and produced into 5,500 orthophoto tiles to create the most comprehensive, high resolution imagery available of this territory. The work follows a similar task completed last year for Waikato. Terralink is aiming to produce detailed photography across the entire country as part of its National Imagery Acquisition Project.

The ortho-images produced from the aerial work are a map-accurate photograph and can be used by local authorities for building permit and resource consent work, soil studies and land use analysis, vegetation classification and pest management, data overlay of roads and boundaries and other asset management responsibilities.

The mapping would also be vitally useful during civil defence emergencies like February's North Island flooding. If such detailed data was available it could be used to estimate which properties and infrastructure throughout a region would be affected by rising flood waters and overlayed across each area to pinpoint houses, sheds, fences and other property either underwater or washed away.

Terralink CEO, Mike Donald, says Terralink has worked for about a year to put together the South Island consortium that will use the new data in a myriad of ways and also benefit from the cost savings achieved by sharing in the project.

The work is important for rural New Zealand which is mostly without high resolution imagery, although Mr Donald says some urban areas do have similar information available.

Feedback from Waikato local authorities on last year's project in that region showed the highly detailed imagery was being used as general context background on web GIS maps, adding significant visual and locational value, resolving matches between CRS and VNZ, for plant pest eradication maps, flight planning for spectral analysis of plant pests and tree conservation strategies, to validate the accuracy of previously captured mapping, digitising and correcting various boundaries, drainages, pump locations, floodgate locations and coastal lines. Uses for the Digital Terrain Model (DTM), which can be provided from the base data includes hydro modeling, flood plain analysis, slope and aspect calculations, erosion studies, gradient calculations and 3D avi file creation, when used in conjunction with satellite or aerial imagery.

Terralink's Imagery Manager, Dave Froggatt, says other benefits, particularly in rural areas, is the reduction in the need for interpretation of vector and symbology information.

The aerial photography work will be particularly challenging because of the South Island's diverse altitude and terrain. The planes will fly a total of 30 runs, some up to 600km long. The photos will be digitally scanned, knitted together and matched up with GPS (Global Positioning System) co-ordinates of known points on the ground.

When Terralink achieves its aim of providing such data across all New Zealand it will result in seamless, integrated imagery, instead of the existing piecemeal, fragmented information.

The complete coverage will become an important platform for GIS (Geographic Information System) use, linking in with satellite imagery, such as that from the Quick Bird satellite which flies over New Zealand every three days. Comparisons of data would give fast and easy analysis of the extent of any land use and environmental changes.

Terralink says the aerial work is likely to continue into next year. The changing angle of the winter sun restricts aerial photography work to an August-to-April flying season and the area is too large to cover before the end of this season, although a stable high pressure weather pattern might permit the work to be completed this year.