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third_party/sqlite/ext/rtree/README

-
-This directory contains an SQLite extension that implements a virtual 
-table type that allows users to create, query and manipulate r-tree[1] 
-data structures inside of SQLite databases. Users create, populate 
-and query r-tree structures using ordinary SQL statements.
-
-    1.  SQL Interface
-
-        1.1  Table Creation
-        1.2  Data Manipulation
-        1.3  Data Querying
-        1.4  Introspection and Analysis
-
-    2.  Compilation and Deployment
-
-    3.  References
-
-
-1. SQL INTERFACE
-
-  1.1 Table Creation.
-
-    All r-tree virtual tables have an odd number of columns between
-    3 and 11. Unlike regular SQLite tables, r-tree tables are strongly 
-    typed. 
-
-    The leftmost column is always the pimary key and contains 64-bit 
-    integer values. Each subsequent column contains a 32-bit real
-    value. For each pair of real values, the first (leftmost) must be 
-    less than or equal to the second. R-tree tables may be 
-    constructed using the following syntax:
-
-      CREATE VIRTUAL TABLE <name> USING rtree(<column-names>)
-
-    For example:
-
-      CREATE VIRTUAL TABLE boxes USING rtree(boxno, xmin, xmax, ymin, ymax);
-      INSERT INTO boxes VALUES(1, 1.0, 3.0, 2.0, 4.0);
-
-    Constructing a virtual r-tree table <name> creates the following three
-    real tables in the database to store the data structure:
-
-      <name>_node
-      <name>_rowid
-      <name>_parent
-
-    Dropping or modifying the contents of these tables directly will
-    corrupt the r-tree structure. To delete an r-tree from a database,
-    use a regular DROP TABLE statement:
-
-      DROP TABLE <name>;
-
-    Dropping the main r-tree table automatically drops the automatically
-    created tables. 
-
-  1.2 Data Manipulation (INSERT, UPDATE, DELETE).
-
-    The usual INSERT, UPDATE or DELETE syntax is used to manipulate data
-    stored in an r-tree table. Please note the following:
-
-      * Inserting a NULL value into the primary key column has the
-        same effect as inserting a NULL into an INTEGER PRIMARY KEY
-        column of a regular table. The system automatically assigns
-        an unused integer key value to the new record. Usually, this
-        is one greater than the largest primary key value currently
-        present in the table.
-
-      * Attempting to insert a duplicate primary key value fails with
-        an SQLITE_CONSTRAINT error.
-
-      * Attempting to insert or modify a record such that the value
-        stored in the (N*2)th column is greater than that stored in
-        the (N*2+1)th column fails with an SQLITE_CONSTRAINT error.
-
-      * When a record is inserted, values are always converted to 
-        the required type (64-bit integer or 32-bit real) as if they
-        were part of an SQL CAST expression. Non-numeric strings are
-        converted to zero.
-
-  1.3 Queries.
-
-    R-tree tables may be queried using all of the same SQL syntax supported
-    by regular tables. However, some query patterns are more efficient
-    than others.
-
-    R-trees support fast lookup by primary key value (O(logN), like 
-    regular tables).
-
-    Any combination of equality and range (<, <=, >, >=) constraints
-    on spatial data columns may be used to optimize other queries. This
-    is the key advantage to using r-tree tables instead of creating 
-    indices on regular tables.
-
-  1.4 Introspection and Analysis.
-
-    TODO: Describe rtreenode() and rtreedepth() functions.
-
-
-2. COMPILATION AND USAGE
-
-  The easiest way to compile and use the RTREE extension is to build
-  and use it as a dynamically loadable SQLite extension. To do this
-  using gcc on *nix:
-
-    gcc -shared rtree.c -o libSqliteRtree.so
-
-  You may need to add "-I" flags so that gcc can find sqlite3ext.h
-  and sqlite3.h. The resulting shared lib, libSqliteRtree.so, may be
-  loaded into sqlite in the same way as any other dynamicly loadable
-  extension.
-
-
-3. REFERENCES
-
-  [1]  Atonin Guttman, "R-trees - A Dynamic Index Structure For Spatial 
-       Searching", University of California Berkeley, 1984.
-
-  [2]  Norbert Beckmann, Hans-Peter Kriegel, Ralf Schneider, Bernhard Seeger,
-       "The R*-tree: An Efficient and Robust Access Method for Points and
-       Rectangles", Universitaet Bremen, 1990.