私はPostgresとSQLを初めて使用します。ある点から最も近い線上の投影された点に線を引く次のスクリプトを作成しました。同じ行数の5〜10ポイントの小さなデータセットで正常に機能します。ただし、2,000行の60ポイントで実行すると、クエリには約12時間かかります。これは、 http：//www.bostongis.com/downloads/pgis_nn.txtからも下に貼り付けられた最近傍関数に基づいています
pgis_fn_nnの編集ドキュメントはhttp://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_nearest_neighbor_genericで入手できます。
遅い部分はpgis_fn_nn（...）の実装です
- 私は何が間違っているのですか？
- これを高速化するためのヒントはありますか？
- 両方のスクリプトを改善する方法はありますか？
- 両方のクエリを1つにまとめたい場合、何をお勧めしますか？
my_script.sql
-- this sql script creates a line table that connects points from a point table
-- to the projected points from the nearest line to the point of oritin
-- delete duplicate tables if they exist
DROP TABLE exploded_roads;
DROP TABLE projected_points;
DROP TABLE lines_from_centroids_to_roads;
-- create temporary exploaded lines table
CREATE TABLE exploded_roads (
the_geom geometry,
edge_id serial
);
-- insert the linestring that are not multistring
INSERT INTO exploded_roads
SELECT the_geom
FROM "StreetCenterLines"
WHERE st_geometrytype(the_geom) = 'ST_LineString';
-- insert the linestrings that need to be converted from multi string
INSERT INTO exploded_roads
SELECT the_geom
FROM (
SELECT ST_GeometryN(
the_geom,
generate_series(1, ST_NumGeometries(the_geom)))
AS the_geom
FROM "StreetCenterLines"
)
AS foo;
-- create projected points table with ids matching centroid table
CREATE TABLE projected_points (
the_geom geometry,
pid serial,
dauid int
);
-- Populate Table
-- code based on Paul Ramsey's site and Boston GIS' NN code
INSERT INTO projected_points(the_geom, dauid)
SELECT DISTINCT ON ("DAUID"::int)
(
ST_Line_Interpolate_Point(
(
SELECT the_geom
FROM exploded_roads
WHERE edge_id IN
(
SELECT nn_gid
FROM pgis_fn_nn(centroids.the_geom, 30000000, 1,10, 'exploded_roads', 'true', 'edge_id', 'the_geom')
)
),
ST_Line_Locate_Point(
exploded_roads.the_geom,
centroids.the_geom
)
)
),
(centroids."DAUID"::int)
FROM exploded_roads, fred_city_o6_da_centroids centroids;
-- Create Line tables
CREATE TABLE lines_from_centroids_to_roads (
the_geom geometry,
edge_id SERIAL
);
-- Populate Line Table
INSERT INTO lines_from_centroids_to_roads(
SELECT
ST_MakeLine( centroids.the_geom, projected_points.the_geom )
FROM projected_points, fred_city_o6_da_centroids centroids
WHERE projected_points.dauid = centroids.id
);
http://www.bostongis.com/downloads/pgis_nn.txtのpgis_fn_nn
---LAST UPDATED 8/2/2007 --
CREATE OR REPLACE FUNCTION expandoverlap_metric(a geometry, b geometry, maxe double precision, maxslice double precision)
RETURNS integer AS
$BODY$
BEGIN
FOR i IN 0..maxslice LOOP
IF expand(a,maxe*i/maxslice) && b THEN
RETURN i;
END IF;
END LOOP;
RETURN 99999999;
END;
$BODY$
LANGUAGE 'plpgsql' IMMUTABLE;
CREATE TYPE pgis_nn AS
(nn_gid integer, nn_dist numeric(16,5));
CREATE OR REPLACE FUNCTION _pgis_fn_nn(geom1 geometry, distguess double precision, numnn integer, maxslices integer, lookupset varchar(150), swhere varchar(5000), sgid2field varchar(100), sgeom2field varchar(100))
RETURNS SETOF pgis_nn AS
$BODY$
DECLARE
strsql text;
rec pgis_nn;
ncollected integer;
it integer;
--NOTE: it: the iteration we are currently at
--start at the bounding box of the object (expand 0) and move up until it has collected more objects than we need or it = maxslices whichever event happens first
BEGIN
ncollected := 0; it := 0;
WHILE ncollected < numnn AND it <= maxslices LOOP
strsql := 'SELECT currentit.' || sgid2field || ', distance(ref.geom, currentit.' || sgeom2field || ') as dist FROM ' || lookupset || ' as currentit, (SELECT geometry(''' || CAST(geom1 As text) || ''') As geom) As ref WHERE ' || swhere || ' AND distance(ref.geom, currentit.' || sgeom2field || ') <= ' || CAST(distguess As varchar(200)) || ' AND expand(ref.geom, ' || CAST(distguess*it/maxslices As varchar(100)) || ') && currentit.' || sgeom2field || ' AND expandoverlap_metric(ref.geom, currentit.' || sgeom2field || ', ' || CAST(distguess As varchar(200)) || ', ' || CAST(maxslices As varchar(200)) || ') = ' || CAST(it As varchar(100)) || ' ORDER BY distance(ref.geom, currentit.' || sgeom2field || ') LIMIT ' ||
CAST((numnn - ncollected) As varchar(200));
--RAISE NOTICE 'sql: %', strsql;
FOR rec in EXECUTE (strsql) LOOP
IF ncollected < numnn THEN
ncollected := ncollected + 1;
RETURN NEXT rec;
ELSE
EXIT;
END IF;
END LOOP;
it := it + 1;
END LOOP;
END
$BODY$
LANGUAGE 'plpgsql' STABLE;
CREATE OR REPLACE FUNCTION pgis_fn_nn(geom1 geometry, distguess double precision, numnn integer, maxslices integer, lookupset varchar(150), swhere varchar(5000), sgid2field varchar(100), sgeom2field varchar(100))
RETURNS SETOF pgis_nn AS
$BODY$
SELECT * FROM _pgis_fn_nn($1,$2, $3, $4, $5, $6, $7, $8);
$BODY$
LANGUAGE 'sql' STABLE;