Mercurial > gemma
diff schema/isrs_functions.sql @ 2987:524f1382558a
Make snapping of many axis segments faster
Since a CTE is materialized anyhow, make the one for the UTM projected
axis a temporary table, extended by the precalculated geometry
boundaries and a spatial index on these, which then can be used in
geometry comparisons within the recursive CTE. This makes snapping
several hundreds of segments faster by more than an order of magnitude
at the expense of longer runtime for snapping only very few segments,
because of the additional cost for index creation. This could be
further optimized by first checking if there is a direct match without
any snapping, but since the function is currently only used in import
processes, a runtime of a few seconds seems acceptable.
author | Tom Gottfried <tom@intevation.de> |
---|---|
date | Wed, 10 Apr 2019 10:02:07 +0200 |
parents | 974122125a76 |
children | 453f15ba8030 |
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--- a/schema/isrs_functions.sql Tue Apr 09 18:48:16 2019 +0200 +++ b/schema/isrs_functions.sql Wed Apr 10 10:02:07 2019 +0200 @@ -54,22 +54,27 @@ -- in m, up to which linestrings will be connected at their boundary ) RETURNS geometry AS $$ +DECLARE z int; DECLARE result_geom geometry; BEGIN + -- Find best matchting UTM zone + z = best_utm(stretch); + + CREATE TEMP TABLE axis AS + SELECT id, wtwaxs, ST_Boundary(wtwaxs) AS bdr + FROM (SELECT id, ST_Transform(wtwaxs::geometry, z) AS wtwaxs + FROM waterway.waterway_axis) AS axs; + CREATE INDEX axs_bdr ON axis USING GiST (bdr); + ANALYZE axis; + WITH RECURSIVE - utm_zone AS ( - -- Find best matchting UTM zone - SELECT best_utm(stretch) AS z), - axis AS ( - SELECT id, ST_Transform(wtwaxs::geometry, z) AS wtwaxs - FROM waterway.waterway_axis, utm_zone), -- In order to guarantee the following ST_Covers to work, -- snap distance mark coordinates to axis points0 AS ( SELECT ST_ClosestPoint( wtwaxs, ST_Transform(geom, z)) AS geom - FROM ST_Dump(ISRSrange_points(stretch)), utm_zone, ( + FROM ST_Dump(ISRSrange_points(stretch)), ( SELECT ST_Collect(wtwaxs) AS wtwaxs FROM axis) AS ax), -- Ensure two distinct points on axis have been found @@ -96,19 +101,19 @@ UNION -- Fill eventual gap SELECT ST_ShortestLine( - ST_Boundary(refgeom), ST_Boundary(geom)) + ST_Boundary(refgeom), bdr) UNION -- Linestring to be added SELECT geom))) FROM axis_snapped AS axis_snapped (refids, refgeom), - axis AS axis (id, geom), + axis AS axis (id, geom, bdr), (SELECT ST_Collect(points.geom) AS pts FROM points) AS points WHERE id <> ALL(refids) AND ST_DWithin( - ST_Boundary(refgeom), ST_Boundary(geom), tolerance) + ST_Boundary(refgeom), bdr, tolerance) AND NOT ST_Covers(ST_Buffer(refgeom, 0.0001), points.pts) - ORDER BY ST_Distance(ST_Boundary(refgeom), ST_Boundary(geom)) + ORDER BY ST_Boundary(refgeom) <-> bdr FETCH FIRST ROW ONLY)), axis_segment AS ( -- Fetch end result from snapping @@ -135,11 +140,17 @@ FROM points) AS fractions GROUP BY axis_segment.line; + -- Drop temporary table to avoid side effects on PostgreSQL's MVCC, + -- because otherwise subsequent invocations of the function will not see + -- changes on the underlying waterway.waterway_axis that might have + -- occured. + DROP TABLE axis; + RETURN result_geom; END; $$ LANGUAGE plpgsql - STABLE PARALLEL SAFE; + PARALLEL RESTRICTED; -- Clip an area to a stretch given by a geometry representing an axis (e.g. -- the output of ISRSrange_axis()).