The Semantic Information of Images Acquired by Aerial Digital Sensors in Cartographic and Environmental Applications

Aerial digital cameras were first presented on the occasion of the ISPRS International Symposium in 2000. Since then, several papers that analyse the geometrical accuracy of digital camera have been presented. These works have underlined the fact that the geometric accuracy obtainable with the digital sensor is significantly higher than the accuracy achieved with scanned analogue cameras. Nevertheless, this accuracy is usually obtained considering predefined markers which allow higher geometric precision than the other points required in the Technical Specifications at a certain map scale, whereas precision (during tests) in map productions is focused on common map entities required in Technical Specifications. Furthermore, good geometric precision in triangulation does not guarantee easy stereoplotting of all the map entities with the required precision. However, it is obviously wrong (and simplistic) to consider, without any logical proof, that digital camera products are comparable, from a semantic point of view, with traditional photogrammetric camera products acquired approximately at the same nominal scale. The semantic information of digital images is accurately analyzed in this paper, and the geometrical aspect is neglected. In particular, the semantic information is considered both from a qualitative and quantitative point of view and the image quality and information content of several digital sensors (ADS40 Leica Geosystems 1st and 2nd Generation, DMC Intergraph Z/I, UltraCamD Vexcel Corp., 3-Das-1 Wehrli & Associates), which are commonly employed in the map production at different scales, are evaluated. In this analysis, particular attention is paid to the handiness of the interpretation of the entities that are requested in modern technical specifications (at several scales) for map production.