orthophotographs

An orthophotograph, or orthophoto, is an aerial photograph that has been geometrically corrected so that the scale is uniform across the entire image. This process removes distortions caused by camera tilt, lens effects, and terrain relief, producing a photo that can be used as a map with accurate measurements.

Orthophotographs are produced through orthorectification, which combines the captured imagery with a model of the terrain, typically a digital elevation model, and information about the sensor geometry. Ground control points or precise sensor positioning data may be used to improve accuracy. The result is a georeferenced image with a constant scale, allowing direct measurement of distances, areas, and features from the photograph.

Orthophotos are distinct from raw, unrectified aerial photographs and from mosaic products. An orthomosaic is a seamless collection of orthophotos that have been stitched together, while an orthophoto refers to a single rectified image. Radiometric corrections may also be applied to improve color and brightness consistency.

Common uses include map production, geographic information systems (GIS) analysis, land surveying, urban planning, environmental monitoring, and cadastral work. Accuracy depends on the quality of the elevation model and control data, and can be limited by occlusions, fast terrain change, or vegetation and water bodies that obscure the underlying surface.

Orthophotographs are often stored with georeferencing information in standard geographic or projected coordinate systems, facilitating integration with other spatial datasets.