Ortofoto

An ortofoto, also called orthophoto or orthophotograph, is a georeferenced aerial image that has been geometrically corrected so that the scale is uniform across the image. In an ortofoto, distortions caused by terrain relief, sensor tilt, and lens distortion are removed through orthorectification, typically using a digital elevation model and sensor geometry. The result is an image in which distances measured on the photograph correspond to true ground distances, allowing reliable overlay with map data and accurate measurements.

Creation: Orthoimages are generated from overlapping photographs captured by airplanes or drones. The process uses ground control points or precise GPS/IMU data, camera calibration, and a digital elevation model to reproject each image onto a common map projection, removing parallax effects. The resulting dataset can be an orthomosaic when multiple frames are stitched into a seamless, georeferenced image.

Applications: Orthophotos are foundational in cartography, GIS, and surveying. They are used for cadastral mapping, urban planning, transportation networks, forestry and agriculture, environmental monitoring, and disaster response, enabling measurement of distances, areas, and features with known accuracy.

Data and accuracy: Orthophotos are delivered in georeferenced formats such as GeoTIFF, JPEG2000, or similar, with embedded projection information. Accuracy depends on input data quality, ground control or GPS/IMU data, and DEM precision, typically ranging from sub-meter to a few meters for large-area projects. Limitations include occlusions, shadows, vegetation cover, changing scenes, and DEM or control-point errors.