Accuracy Checks in the Production of Orthophotos

Abstract

Orthophotos have been used extensively in many applications today. In an attempt to map the earth’s surface in a shortest possible time and provide information for monitoring and planning, Orthophotos have proved reliable as far as these are concerned. Orthophotos are one of the most important base layers of data for GIS systems. The use of Orthophotos in a GIS often implies seamless image data. The major advantage of Orthophotos is their ability to be produced in a short time to provide up-to-date information for urgent planning. They are also produced at a less expensive production price than line or vector maps.

The need therefore for quick and reliable data for many rising applications has led to the development in this technology and hence finding ways to make it better in terms of its appearance (radiometric enhancements) and geometric accuracy.This paper looks at the creation of an Orthophoto and enumerates the factors that ensure the geometric accuracy of the Orthophoto.

Users of Orthophotos must understand that to make measurements on an Orthophoto, oneneeds to know the quality of the underlying surface description since this affects the geometric accuracy of the Orthophoto. In this paperthe geometric accuracy  with which an orthophoto is produced is analysed.Accuracies during theorientation of the input image and scanning resolution of the scanned image and accuracy at DTMsstage are considered in this paper.

Keywords: Orthophoto, geometric accuracy, orientation and DTM.