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quadtree |
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A scheme of hierarchical representation of the contents of an image or a raster data set. It is often disadvantageous to assign uniform cells to every part of an image, because this strategy fails to take advantage of uniformity in some parts of the image, and cannot respond to more rapid variation in other parts. A quadtree is constructed by beginning with the entire image, and dividing it into four quadrants. If the image in any of the quadrants shows variation, it is divided again into four. The process continues until no variation exists within any quadrant; or until the process reaches some limit of resolution. The result is a \'tree\', every branching having four shoots, and all branches terminating in a \'leaf\'. Quadtrees can be very efficient for storing certain types of geographic information, and have been widely implemented in geographical information systems. (MG) |
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