Conference Paper

Methods and techniques for the correction of natural shades on aerial-photo or satellite maps

Conference: 20th International Cartographic Conference, At Beijing

ABSTRACT This study examines possible ways first to restrain or even eliminate the "false" shades of the relief, created mainly by the direction of the natural sunlight presented on aerial-photo or satellite images, and then to replace them with the "correct" artificial hill-shading shades according to the cartographic principles of legibility and perceptibility, which allow the map user to easily and clearly interpret the relief's shapes and formations. The natural shades are eliminated from the aerial-photo or satellite images by applying special radiometric and statistical processing in order to create images free of shades. An analytical description of the earth's surface -stored as a digital elevation model-combined with computing tools of a variety of hill-shading methods are used to produce a cartographic "correct" image of shades of the study area. Finally, image-processing techniques are applied to create new images composed by the "correct" shades and the shaded free aerial-photo or satellite images. The outcomes indicate the potential of the incorporated methods and applied techniques in order to construct aerial-photo or satellite maps clearly and legibly perceived. KEY-WORDS: Aerial-photo/satellite maps, relief visualization, hill-shading, illumination models, correction of topographic effect.

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    ABSTRACT: The natural relief shades present in earth’s surface images are affected by physical lighting procedures that take place along the trace of sunlight from the initial radiation to the final capturing by sensors. An analysis of all these combined factors is given in the present paper in order to define their qualitative meaning and evaluate their influence on the variation of tones that forms the relief effect. These efforts are tested both on computational and conceptual level with examples of different lighting conditions on simulated solids. In addition, the qualitative and quantitative approaches of light components are discussed in the context of suggesting a systematic, practical strategy for the selection of the necessary parameters of relief shading for several cartographic products.
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