42 lines
1.8 KiB
PL/PgSQL
42 lines
1.8 KiB
PL/PgSQL
--------------------------------------------------------------------------------
|
|
-- SQL versions of the C database functions.
|
|
--
|
|
-- Pure pl/pgsql versions are *slower* than the C versions, and not recommended
|
|
-- for production use. However, they are significantly easier to install, and
|
|
-- require fewer dependencies.
|
|
--------------------------------------------------------------------------------
|
|
|
|
-- tile_for_point function returns a Morton-encoded integer representing a z16
|
|
-- tile which contains the given (scaled_lon, scaled_lat) coordinate. Note that
|
|
-- these are passed into the function as (lat, lon) and should be scaled by
|
|
-- 10^7.
|
|
--
|
|
-- The Morton encoding packs two dimensions down to one with fairly good
|
|
-- spatial locality, and can be used to index points without the need for a
|
|
-- proper 2D index.
|
|
CREATE OR REPLACE FUNCTION tile_for_point(scaled_lat int4, scaled_lon int4)
|
|
RETURNS int8
|
|
AS $$
|
|
DECLARE
|
|
x int8; -- quantized x from lon,
|
|
y int8; -- quantized y from lat,
|
|
BEGIN
|
|
x := round(((scaled_lon / 10000000.0) + 180.0) * 65535.0 / 360.0);
|
|
y := round(((scaled_lat / 10000000.0) + 90.0) * 65535.0 / 180.0);
|
|
|
|
-- these bit-masks are special numbers used in the bit interleaving algorithm.
|
|
-- see https://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
|
|
-- for the original algorithm and more details.
|
|
x := (x | (x << 8)) & 16711935; -- 0x00FF00FF
|
|
x := (x | (x << 4)) & 252645135; -- 0x0F0F0F0F
|
|
x := (x | (x << 2)) & 858993459; -- 0x33333333
|
|
x := (x | (x << 1)) & 1431655765; -- 0x55555555
|
|
|
|
y := (y | (y << 8)) & 16711935; -- 0x00FF00FF
|
|
y := (y | (y << 4)) & 252645135; -- 0x0F0F0F0F
|
|
y := (y | (y << 2)) & 858993459; -- 0x33333333
|
|
y := (y | (y << 1)) & 1431655765; -- 0x55555555
|
|
|
|
RETURN (x << 1) | y;
|
|
END;
|
|
$$ LANGUAGE plpgsql IMMUTABLE;
|