Merge remote-tracking branch 'upstream/pull/2383'

[rails.git] / db / functions / functions.sql

diff --git a/db/functions/functions.sql b/db/functions/functions.sql
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+--------------------------------------------------------------------------------
+-- 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;
+
+
+-- maptile_for_point returns an integer representing the tile at the given zoom
+-- which contains the point (scaled_lon, scaled_lat). Note that the arguments
+-- are in the order (lat, lon), and should be scaled by 10^7.
+--
+-- The maptile_for_point function is used only for grouping the results of the
+-- (deprecated?) /changes API call. Please don't use it for anything else, as
+-- it might go away in the future.
+CREATE OR REPLACE FUNCTION maptile_for_point(scaled_lat int8, scaled_lon int8, zoom int4)
+  RETURNS int4
+  AS $$
+DECLARE
+  lat CONSTANT DOUBLE PRECISION := scaled_lat / 10000000.0;
+  lon CONSTANT DOUBLE PRECISION := scaled_lon / 10000000.0;
+  zscale CONSTANT DOUBLE PRECISION := 2.0 ^ zoom;
+  pi CONSTANT DOUBLE PRECISION := 3.141592653589793;
+  r_per_d CONSTANT DOUBLE PRECISION := pi / 180.0;
+  x int4;
+  y int4;
+BEGIN
+  -- straight port of the C code. see db/functions/maptile.c
+  x := floor((lon + 180.0) * zscale / 360.0);
+  y := floor((1.0 - ln(tan(lat * r_per_d) + 1.0 / cos(lat * r_per_d)) / pi) * zscale / 2.0);
+
+  RETURN (x << zoom) | y;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;