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A quadtree does the same thing for two-dimensional space. It takes a rectangular region and divides it into four equal quadrants: northwest, northeast, southwest, southeast. If a quadrant has too many points in it, it subdivides again and again. Each subdivision creates smaller and smaller cells where points are densely packed.
，这一点在Line官方版本下载中也有详细论述
From Sea to Table
"Boys like either dinosaurs or airplanes," he said. "I was very much an airplane boy."