The earth is not flat and undulations in the ground’s terrain surface present as distortions in raw aerial photography. These distortions cause misalignments when comparing the image to an existing map of the same area.
To correct these misalignments, DEPHOS Group aerial survey team converts raw aerial imagery into a product known as an Orthophoto. This is an image that is georeferenced with real-world map coordinates and image pixel is corrected to account for displacements caused by the terrain below the aircraft. Since an aerial image consists of 3D information on the ground being projected onto a 2D image plane, an Orthophoto is produced by compiling a 3D model of the ground surface from adjacent overlapping photos (known as a stereo pair) and applying mathematical routines to adjust pixel values in the new image.
The benefits of an orthophoto lies in the fact that it is a map product that can be understood by many non-mapping specialists. Being re-projected to account for terrain displacements and a uniform map scale means that the orthophoto can further be used to measure true distances, be used as a reference dataset to digitize additional mapping products and be used as a backdrop that provides context to other types of mapped data.