Aerial photography

Text author: Luděk Krtička Last update: 2021-12-16

Aerial photography is the photography of the ground taken from the aircraft or unmanned aerial vehicle (UAV). Of fundamental importance to the quality of aerial photographs is the camera used to obtain the images (Morgan et al., 2010). The image record can be taken in a larger number of spectral bands. Unlike satellite images, aerial photographs offer much higher resolution and legibility of details.

Aerial photography contains a number of distortions that must be corrected to make the photograph usable for mapping. The result of the correction is an orthorectified aerial image, which is an image in which the displacements of image points caused by sensor orientation and ground relief have been removed by orthogonal projection onto a reference surface (Terminological commission of the Czech Office for Surveying, Mapping and Cadastre, n.d.). In many countries orthorectified aerial photograph (orthophoto) is a widely available geographic product with regular renewal.

Orthorectified aerial photographs are very suitable for detailed surveying and mapping projects. They are best used in open or semi-open terrain with low tree cover and for creating sprint maps in urban areas.

Typical problems of aerial photographs are shadows created by high objects (for example trees) in which the details on the surface are hardly recognizable and also tilting of tall buildings caused by central projection, when the tops of buildings are shifted compared to their base. Products labeled as True orthophoto do not have this imperfection. True orthophoto provides a vertical view of the earth’s surface and eliminates the building tilting, but the cost of production is much higher (Buczkowski, 2020).

Overlay of the orienteering map with orthorectified aerial photograph.

High object can create shadows on orthophoto — High objects can create shadows, making it difficult to identify objects hidden in the shadows.

The roofs of the buildings are shifted compared to the base of the building — Due to central projection, the sides of high buildings can be seen in many cases. The roofs of the buildings are thus shifted compared to the base of the building (purple line).

References

Buczkowski, A. (2020, September 7). What is the difference between othophotos, orthophotomaps, orthomosaics and true orthophotos? Geoawesomeness. https://geoawesomeness.com/what-is-the-difference-between-othophotos-orthophotomaps-orthomosaics-and-true-orthophotos/

Morgan, J., Gergel, S., & Coops, N. (2010). Aerial Photography: A Rapidly Evolving Tool for Ecological Management. Bioscience, 60, 47–59. https://doi.org/10.1525/bio.2010.60.1.9

Terminological commission of the Czech Office for Surveying, Mapping and Cadastre. (n.d.). Ortho-image. The Dictionary of Geodesy, Cartography and Cadastre. Retrieved 17 December 2021, from http://www.slovnikcuzk.eu/termin.php?&tid=5991&l=ortho-image