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