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Unformatted text preview: CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Spatial Index Structures (Rtree Family) Instructor: Cyrus Shahabi CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Problem Given a collection of geometric objects (points, lines, polygons, ...) organize them on disk, to answer spatial queries (range, nn, etc) CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Problem Spatial objects Points, lines, rectangles, regions, Hierarchical data structures Based on recursive decomposition, similar to divide and conquer method, like Btree. Why not BTree? More than one dimension Concept of closeness relies on all the dimensions of the spatial data CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Rtrees [Guttman 84] Main idea: extend B+tree to multidimensional spaces! (only deal with Minimum Bounding Rectangles  MBR s) CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Heightbalanced tree similar to Btree for kdimensions Every leaf node contains between m (m M/2) and M index records, unless it is the root For each index record (I, tupleidentifier) in a leaf node, I is the MBR that contains the ndimensional data object represented by the indicated tuple Every nonleaf node has between m and M children unless it is the root For each entry (I, childpointer) in a nonleaf node, I is the MBR that spatially contains the rectangles in the child node. All leaves appear on the same level The root node has at least two children unless it is a leaf CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Example m=2,M=4: group nearby rectangles to parent MBRs; each group > disk page A B C D E F G H J I CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Example m=2, M=4 A B C D E F G H I J P1 P2 P3 P4 F G D E H I J A B C CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Example m=2, M=4 A B C D E F G H I J P1 P2 P3 P4 P1 P2 P3 P4 F G D E H I J A B C CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Rtrees  format of nodes {(MBR; obj_ptr)} for leaf nodes P1 P2 P3 P4 A B C xlow; xhigh ylow; yhigh ... obj ptr ... CSCI585 CSCI585 C. Shahabi CSCI585 CSCI585 Rtrees  format of nodes {(MBR; node_ptr)} for nonleaf nodes P1 P2 P3 P4 A B C xlow; xhigh ylow; yhigh ......
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This document was uploaded on 05/17/2010.
 Spring '09

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