Orthoimagery

Orthoimagery, or orthophotography, is aerial or satellite imagery that has been geometrically corrected so that the scale is uniform across the image and distortions caused by camera tilt, terrain relief, and perspective are removed. The result is a planimetrically accurate representation of the ground, in which each pixel corresponds to a single ground location.

Production of orthoimagery involves several steps. Imagery is acquired from sensors such as cameras on aircraft or satellites. A digital elevation model (DEM) or digital terrain model (DTM) is used to model relief. An orthorectification process applies the sensor geometry, terrain information, and, when available, ground control points or tie points to map each pixel to its true ground coordinates. When multiple images are combined to cover an area, the result is an orthomosaic, a seamless orthoimage.

Accuracy in orthoimagery depends on input data quality, the resolution of the imagery, the accuracy of the DEM, and the density of ground control information. Planimetric accuracy can range from sub-pixel to several meters depending on project conditions and required precision. Terrain complexity and data gaps can influence outcomes.

Orthoimagery serves as a base layer for geographic information systems and is used in cartography, land management, urban planning, environmental monitoring, disaster response, and navigation. Common formats include georeferenced GeoTIFFs and other GIS-ready products, often with metadata describing the coordinate system and accuracy. Licensing varies by source, with some providers offering open data and others restricting use.