Documentation | Help File | Glossary | Orthorectification

The most advanced method of aerial imagery rectification. Orthorectification requires the following information about the image: i) a Digital Elevation Model (DEM) of the subject terrain, ii) the altitude of the camera at the time the image was taken, iii) the focal length of the camera, iv) points of symmetry of the camera lens, and v) either some GCPs or very detailed information about the position of the camera at the instant of the photo, including the longitude and latitude position coordinates and the exact roll, pitch, and yaw of the camera. A DEM is a data set containing detailed altitude information about the subject terrain, with the altitude information organized as cells in a grid with longitude, latitude, and altitude information for each cell.

Orthorectification yields the most accurate rectification results, particularly with aerial photos of terrain with large elevation variations in relation to the position of the camera, provided that the required information relating to the aerial image is available and that the user possesses an advanced knowledge level and the required software tools (which tend to be expensive).