ced8ac86ab
This repo contains code for three functions to be loaded into PostgreSQL as a shared library: 1. `maptile_for_point`, which is used only by the `/changes` API call. This API call is little-used and IMHO should be deprecated and removed. However, even now it's hardly on the hot path for most development activities. 2. `tile_for_point`, which is used only in migrations. At this point, it seems unlikely that anyone will be doing a migration on existing data which would call this function (most developers will be running migrations on an empty database, to set it up). 3. `xid_to_int4`, which is only used for replication using Osmosis and isn't used in the Rails code at all. Hopefully this will be replaced Real Soon Now, but until then it's a quite advanced feature that most developers won't need. Therefore, this patch proposes to replace the above three shared library functions with SQL implementations of the first two. These are _much_ slower - by a factor of about 30x, however this makes no difference when they're run on a completely empty database. In return, we're able to drop a dependency on the PostgreSQL server development package, and clean a few lines out of the installation instructions. It's still possible to make and install the shared library functions, and I've included instructions about how to do that - although it shouldn't be necessary for the vast majority of `openstreetmap-website` developers.
70 lines
2.8 KiB
PL/PgSQL
70 lines
2.8 KiB
PL/PgSQL
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-- SQL versions of the C database functions.
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--
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-- Pure pl/pgsql versions are *slower* than the C versions, and not recommended
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-- for production use. However, they are significantly easier to install, and
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-- require fewer dependencies.
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--------------------------------------------------------------------------------
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-- tile_for_point function returns a Morton-encoded integer representing a z16
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-- tile which contains the given (scaled_lon, scaled_lat) coordinate. Note that
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-- these are passed into the function as (lat, lon) and should be scaled by
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-- 10^7.
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--
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-- The Morton encoding packs two dimensions down to one with fairly good
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-- spatial locality, and can be used to index points without the need for a
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-- proper 2D index.
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CREATE OR REPLACE FUNCTION tile_for_point(scaled_lat int4, scaled_lon int4)
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RETURNS int8
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AS $$
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DECLARE
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x int8; -- quantized x from lon,
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y int8; -- quantized y from lat,
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BEGIN
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x := round(((scaled_lon / 10000000.0) + 180.0) * 65535.0 / 360.0);
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y := round(((scaled_lat / 10000000.0) + 90.0) * 65535.0 / 180.0);
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-- these bit-masks are special numbers used in the bit interleaving algorithm.
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-- see https://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
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-- for the original algorithm and more details.
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x := (x | (x << 8)) & 16711935; -- 0x00FF00FF
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x := (x | (x << 4)) & 252645135; -- 0x0F0F0F0F
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x := (x | (x << 2)) & 858993459; -- 0x33333333
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x := (x | (x << 1)) & 1431655765; -- 0x55555555
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y := (y | (y << 8)) & 16711935; -- 0x00FF00FF
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y := (y | (y << 4)) & 252645135; -- 0x0F0F0F0F
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y := (y | (y << 2)) & 858993459; -- 0x33333333
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y := (y | (y << 1)) & 1431655765; -- 0x55555555
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RETURN (x << 1) | y;
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END;
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$$ LANGUAGE plpgsql IMMUTABLE;
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-- maptile_for_point returns an integer representing the tile at the given zoom
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-- which contains the point (scaled_lon, scaled_lat). Note that the arguments
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-- are in the order (lat, lon), and should be scaled by 10^7.
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--
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-- The maptile_for_point function is used only for grouping the results of the
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-- (deprecated?) /changes API call. Please don't use it for anything else, as
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-- it might go away in the future.
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CREATE OR REPLACE FUNCTION maptile_for_point(scaled_lat int8, scaled_lon int8, zoom int4)
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RETURNS int4
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AS $$
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DECLARE
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lat CONSTANT DOUBLE PRECISION := scaled_lat / 10000000.0;
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lon CONSTANT DOUBLE PRECISION := scaled_lon / 10000000.0;
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zscale CONSTANT DOUBLE PRECISION := 2.0 ^ zoom;
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pi CONSTANT DOUBLE PRECISION := 3.141592653589793;
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r_per_d CONSTANT DOUBLE PRECISION := pi / 180.0;
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x int4;
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y int4;
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BEGIN
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-- straight port of the C code. see db/functions/maptile.c
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x := floor((lon + 180.0) * zscale / 360.0);
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y := floor((1.0 - ln(tan(lat * r_per_d) + 1.0 / cos(lat * r_per_d)) / pi) * zscale / 2.0);
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RETURN (x << zoom) | y;
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END;
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$$ LANGUAGE plpgsql IMMUTABLE;
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