Determining the effects of different scanner and scanning resolutions on orientation errors in producing of Orthophotos

Günay Çakır, Sedat Keleş, Fatih Sivrikaya, Emin Zeki Başkent and Selahattin Köse
Karadeniz Technical University, Faculty of Forestry
61080, Trabzon, Turkey
Tel: +90 462 377 37 34, Fax: +90 462 325 74 99
gcakir@ktu.edu.tr; fatihs@ktu.edu.tr, skeles@ktu.edu.tr, baskent@ktu.edu.tr, skose@ktu.edu.tr

Abstract
An orthophoto is a geo-referenced image produced from aerial photos. It has geometric features of a map and the qualities of photographs, representing all terrain features. Due to its unlimited capability, it can be used in various  areas such as forest management, ecosystem management, environmental planning and social science. The quality of the final orthophoto mainly depends on several major factors such as the accuracy of the Digital Surface Model (DSM), clarity of the air photos, scanning  resolution and quality, Ground Control Point (GCP) accuracy, camera model and mosaicking. The objective of this study is to explain the effects of different scanners and scanning resolutions on spatial accuracy in conversion of analog aerial photos to orthophotos. We selected two different scanners, a normal desktop and photogrammetric. 23 by 23 cm diapositives and 23 by 23 analog photographs of air photos were scanned through desktop scanner with a resolution of 600 dpi. In addition, 23 by 23 cm diapositives of air photos were scanned through photogrammetric scanner with a resolution of 1200 dpi. Orthophotos were created with ERDAS imagine OrthoBASE software. DEM was also used to produce orthophoto images. Results show that orientation errors of digital orthophoto generation for diapositives and  analog photographs, scanned with a desktop scanner, are 2 – 3 pixels and 10 – 11 pixels, respectively, whereas the errors of diapositives, scanned with the photogrammetric scanner, are 0.1 – 0.3 pixels.

Keywords: orthophoto, accuracy, digital image processing, forest management

In: Caetano, M. and Painho, M. (eds). Proceedings of the 7th International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, 5 – 7 July 2006, Lisboa, Instituto Geográfico Português

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