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Spatial Join Yan Huang huangyan@unt.edu

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Spatial Join Given two sets of spatial data Find the pair of objects satisfying certain spatial predicate – e.g. INSIDE, WITHIN

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Two Methods On-the-fly Indexing-based

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On-the-fly Nested-loop Block-nested-loop for large dataset

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Indexing: Z-order Grid the space Create a z-order of the cells An object is represented by MBR and have a set of z-values Index z-values using on-dimensional indexing such as B+ tree INSIDE? WITHIN?

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Filter-and-refine Each object is represented by it MBR Join in MBR level first Only those past MBR level filtering will be check for actually relationship INSIDE? WITHIN?

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R-tree indexing from wikipedia

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Quadtree From wikipedia

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Tree-matching Simultaneously traverse two tree nodes TreeM(R1,R2) If the two nodes are non-disjoint – If R1 is leaf R2 is not leaf, recursively call TreeM(R1,R2.child) for each child of R2. Otherwise, find pairs from R1 and R2 – Otherwise If R2 is leaf, recursively call TreeM(R1.child,R2) for each child of R1. Otherwise, recursively call TreeM(R1.child,R2.child) for each child of R1 and each child of R2.

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Partition-based Merge Join Jignesh M. Patel, David J. DeWitt, Partition Based Spatial-Merge Join, SIGMOD 1996.

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