GENERATION OF TRUE ORTHOIMAGES FROM AIRBORNE SCANNER DATA WITHOUT THE NEED OF HEIGHT INFORMATION

摘要

This paper presents a new technique for the efficient production of true orthoimages. The approach is based on airborne scanner data, and takes advantage of the particular geometric properties of such data. If scanner data are available, that are acquired in two flight lines perpendicular to each other, no height information is required to generate true orthoimages. In airborne pushbroom scanner systems one sensor line is looking to the nadir and is adjusted perpendicular to the flight track. The data acquired by the nadir channel follow a mixed geometry. In flight direction the mapped area is imaged in parallel projection. Across to the flight line the terrain is imaged in central projection. In other words, in flight direction, object points recorded are not displaced due to their height, but mapped in a correct position. On the other hand point displacements because of object heights occur only crosswise to the flight directions scene is imaged twice in flight lines perpendicular to each other, the first image strip provides correct ground coordinates of any object in one direction, the second image strip in the other direction. The new approach takes advantage of these particular geometric properties. It is based on the definition of corresponding points in the image data sets by means of matching techniques. Each conjugate point directly provides the correct ground coordinates and can be assigned as a pixel to the orthoimage. Thus, a true orthoimage is generated without any knowledge of the object heights or further calculations. The paper provides a detailed description of the approach, and its advantages and limitations are discussed.