Mosaicking of orthorectified aerial images

Aerial photographs are widely used in surveying, geographic information systems (GIS), and other applications. Analysis of a large area requires the creation of an image mosaic, which is composed of several aerial photographs. In an ideal situation, a perfect mosaic can be generated using a series of rigid transformations on the source images. In practice, geometric distortions and radiometric differences interfere with the mosaicking process. In this paper a complete algorithm to mosaic images taken at different times and conditions with geometric distortions and radiometric differences is presented. The algorithm, which works without any human intervention, integrates global feature matching algorithms into the process of selecting a seam line. The algorithm may be applied to mosaic any set of images for which an appropriate matching algorithm exists. The creation of an image mosaic is accomplished using local transformations along a computed seam line and a rigid transformation elsewhere. An automatic stereo matching algorithm, originally developed for surface height measurement, is used to detect matching pairs of tie points across frame boundaries. These tie points are used to compute the seam line for the mosaic, and to compute geometric and radiometric correcting transformations around this seam line.