Integrated Dem and Pan-sharpened Spot-4 Image in Urban Studies

Digital orthoimages are becoming increasingly of interest as they provide up-to-date information for a wide range of applications. Facing the need for accurate spatial information this paper aims to the production of orthoimages and their further processing, as well as to the three dimensional visualization of the resulting images. The data used are one panchromatic image from Spot-3, with spatial analysis 10 m, and one multispectral from Spot-4, with spatial analysis 20 m. Both images depict the city of Thessaloniki, in Greece. In order to eliminate distortions arising from the topographic relief and improve the accuracy of orthoimages, a DTM (Digital Terrain Model) of the same area with grid size of 25 meters was used. It should be noted that the ground control points were collected by GPS measurements and two orthophotos, which were produced from 1:10,000 and 1:20,000 aerial photos. Furthermore, the panchromatic orthoimage and the multispectral orthoimage were fused with the methodology of principal components analysis. Prior to the fusion process, the registration of the image with the lower spatial analysis (the multispectral) on the image with the higher spatial analysis (the panchromatic) was necessary. In order to analyze the reliability and the accuracy of the spectral and spatial information of the synthetic image an evaluation was accomplished based on statistical tests. Additionally, supervised classification was made in the synthetic image and its accuracy was evaluated. Finally, a panoramic video was created which included a supervised flight through the area of interest for the virtual representation of the anaglyph.