65 lines
1.6 KiB
PL/PgSQL
65 lines
1.6 KiB
PL/PgSQL
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-- {
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-- Return pixel resolution at the given zoom level
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-- }{
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CREATE OR REPLACE FUNCTION CDB_XYZ_Resolution(z INTEGER)
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RETURNS FLOAT8
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AS $$
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-- circumference divided by 256 is z0 resolution, then divide by 2^z
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SELECT 6378137.0*2.0*pi() / 256.0 / power(2.0, z);
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$$ LANGUAGE SQL IMMUTABLE STRICT;
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-- }
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-- {
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-- Returns a polygon representing the bounding box of a given XYZ tile
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--
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-- SRID of the returned polygon is forceably 3857
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--
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-- }{
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CREATE OR REPLACE FUNCTION CDB_XYZ_Extent(x INTEGER, y INTEGER, z INTEGER)
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RETURNS GEOMETRY
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AS $$
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DECLARE
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origin_shift FLOAT8;
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initial_resolution FLOAT8;
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tile_geo_size FLOAT8;
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pixres FLOAT8;
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xmin FLOAT8;
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ymin FLOAT8;
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xmax FLOAT8;
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ymax FLOAT8;
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earth_circumference FLOAT8;
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tile_size INTEGER;
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BEGIN
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-- Size of each tile in pixels (1:1 aspect ratio)
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tile_size := 256;
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initial_resolution := CDB_XYZ_Resolution(0);
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--RAISE DEBUG 'Initial resolution: %', initial_resolution;
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origin_shift := (initial_resolution * tile_size) / 2.0;
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-- RAISE DEBUG 'Origin shift (after): %', origin_shift;
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pixres := initial_resolution / (power(2,z));
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--RAISE DEBUG 'Pixel resolution: %', pixres;
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tile_geo_size = tile_size * pixres;
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--RAISE DEBUG 'Tile_geo_size: %', tile_geo_size;
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xmin := -origin_shift + x*tile_geo_size;
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xmax := -origin_shift + (x+1)*tile_geo_size;
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--RAISE DEBUG 'xmin: %', xmin;
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--RAISE DEBUG 'xmax: %', xmax;
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ymin := origin_shift - y*tile_geo_size;
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ymax := origin_shift - (y+1)*tile_geo_size;
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--RAISE DEBUG 'ymin: %', ymin;
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--RAISE DEBUG 'ymax: %', ymax;
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RETURN ST_MakeEnvelope(xmin, ymin, xmax, ymax, 3857);
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END
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$$ LANGUAGE 'plpgsql' IMMUTABLE STRICT;
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-- }
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