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------------------------------------------------------------------------------
--
-- Create grid for splitting up Mercator polygons.
--
------------------------------------------------------------------------------
-- speed up spatialite processing
PRAGMA journal_mode = OFF;
PRAGMA synchronous = OFF;
PRAGMA temp_store = MEMORY;
PRAGMA cache_size = 5000000;
-- make sure we have the SRID in the spatial_ref_sys table
SELECT InsertEpsgSrid(3857) WHERE (SELECT count(*) FROM spatial_ref_sys WHERE srid = 3857) = 0;
-- clean up if this is left over from previous run
SELECT DiscardGeometryColumn('grid', 'geometry') FROM geometry_columns WHERE f_table_name='grid';
DROP TABLE IF EXISTS grid;
CREATE TABLE tmp_square_grid (id INTEGER PRIMARY KEY AUTOINCREMENT);
SELECT AddGeometryColumn('tmp_square_grid', 'geometry', 3857, 'MULTIPOLYGON', 'XY');
INSERT INTO tmp_square_grid (geometry)
SELECT ST_SquareGrid(
-- slightly smaller than the full extent so we don't get an
-- extra set of tiles at the top and right boundary
BuildMbr(-20037508.34, -20037508.34, 20037508.0, 20037508.0, 3857),
-- split into 64x64 tiles
2*20037508.34/64);
.elemgeo tmp_square_grid geometry tmp_square_grid_elem id_new id;
CREATE TABLE grid (OGC_FID INTEGER PRIMARY KEY AUTOINCREMENT);
SELECT AddGeometryColumn('grid', 'geometry', 3857, 'POLYGON', 'XY');
INSERT INTO grid (geometry)
SELECT ST_Intersection(
-- 50 units overlap on each side of the tile
ST_Expand(geometry, 50.0),
-- make sure there are no overlaps at the sides
BuildMbr(-20037508.34, -20037508.34, 20037508.34, 20037508.34, 3857))
FROM tmp_square_grid_elem;
SELECT CreateSpatialIndex('grid', 'geometry');
SELECT DiscardGeometryColumn('tmp_square_grid', 'geometry');
DROP TABLE tmp_square_grid;
SELECT DiscardGeometryColumn('tmp_square_grid_elem', 'geometry');
DROP TABLE tmp_square_grid_elem;
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