Orthophotography

OSNI creates orthophotographs of Northern Ireland from high quality aerial images with distortions removed. Orthophotographs give a scale-accurate bird's eye view of the landscape from which accurate measurements can be taken.

Orthophotography is supplied either as pre-determined tiles or as a bespoke clip out centred on a site-specific area.

How orthophotography is obtained

Orthophotograph tile layout follows OSNI 1:10,000 scale mapping layout.  Complete coverage of Northern Ireland orthophotography is flown in three year cycles. 

There are some water-based tiles along the coast and the southern shore of Lough Neagh which aren't updated.

Key features

  • photographs are taken in good  weather conditions to provide the best possible images using a large format (196 megapixel) digital camera
  • distortions caused by camera tilt and topographical relief are removed by an orthorectification process for a scale accurate image
  • orthophotography is an actual image, rather than a representation, and can provide information such as shape, size patterns, shadows, colour and texture
  • OSNI orthorectified photography can be used by itself or along with other data displayed in the Irish Grid Co-ordinate system

Applications

  • base mapping for GIS
  • urban planning
  • watershed analysis
  • civil engineering
  • environmental assessment
  • engineering design
  • asset management
  • municipal and government maps
  • right-of-way mapping
  • public and private land development

Technical information

  • each pixel represents a real world distance of 16cm (digital) and 25cm (film)
  • photographs are taken from an altitude of 5,000 feet above ground level
  • fully geo-referenced digital orthophotography is available in ecw and jpeg formats
  • average file size of each tile is 19.7MB (ecw digital) and 9.8MB (ecw film)
  • orthophotograph tile layout follows OSNI 1:10,000 scale mapping layout
  • area covered by each tile is  2.4km x 1.6km
  • bespoke user defined area available

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