kopia lustrzana https://github.com/openmaptiles/openmaptiles
Simplify landcover layer generalisation SQL (#1255)
I was reading through the SQL used to generalise the landcover layer ([`layers/landcover/generalized.sql`](pull/1262/head596f44aa26/layers/landcover/generalized.sql)) and I noticed that when creating the generalised landcover tables for zooms 9-13, the SQL was doing something like this: ```sql SELECT * FROM simplify_vw_z13 WHERE ST_NPoints(geometry) < 50 UNION ALL SELECT * FROM simplify_vw_z13 WHERE ST_NPoints(geometry) >= 50 AND ST_NPoints(geometry) < 300 ``` As in, the simplification/clustering of landcover generalisations was being done in two steps: once for polygons with fewer than fifty points, and once for polygons with 50+ points. As far as I can see, there's no benefit to doing this — it's probably just an artefact of the dev work done for the [original pull request](https://github.com/openmaptiles/openmaptiles/pull/1035). Of course, I might be completely missing the reason for clustering polygons into two groups (<50 points and 50+ points). But assuming I haven't, I've created this pull request to simplify the SQL used in the generalisation, merging the two steps into something like this: ```sql SELECT * FROM simplify_vw_z13 WHERE ST_NPoints(geometry) < 300 ``` The effect is to slightly reduce the number of landcover features (polygons with <50 points can now be clustered/unioned with those 50+), and to reduce the time taken to generalise the landcover tables (in a small test using OSM's Iceland data I saw a 7% reduction in the time spent). It doesn't alter the features that are shown on the map. Builds upon work from commits4a1b0afa26andda689f9e42.
Matt Riggott
GitHub
rodzic
91c6d3bbd1
commit
4d6945b935
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@ -29,26 +29,12 @@ CREATE INDEX ON simplify_vw_z13 USING GIST (geometry);
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-- etldoc: simplify_vw_z13 -> osm_landcover_gen_z13
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CREATE TABLE osm_landcover_gen_z13 AS
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(
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SELECT subclass,
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ST_MakeValid(
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(ST_dump(
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ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z13
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WHERE ST_NPoints(geometry) < 50
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AND subclass IN ('wood', 'forest')) union_geom50
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GROUP BY subclass,
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cid
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UNION ALL
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SELECT subclass, ST_MakeValid((ST_dump(ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z13
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WHERE ST_NPoints(geometry) >= 50
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AND ST_NPoints(geometry) < 300
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WHERE ST_NPoints(geometry) < 300
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AND subclass IN ('wood', 'forest')) union_geom300
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GROUP BY subclass,
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cid
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@ -79,26 +65,12 @@ CREATE INDEX ON simplify_vw_z12 USING GIST (geometry);
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-- etldoc: simplify_vw_z12 -> osm_landcover_gen_z12
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CREATE TABLE osm_landcover_gen_z12 AS
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(
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SELECT subclass,
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ST_MakeValid(
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(ST_dump(
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ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z12
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WHERE ST_NPoints(geometry) < 50
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AND subclass IN ('wood', 'forest')) union_geom50
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GROUP BY subclass,
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cid
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UNION ALL
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SELECT subclass, ST_MakeValid((ST_dump(ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z12
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WHERE ST_NPoints(geometry) >= 50
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AND ST_NPoints(geometry) < 300
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WHERE ST_NPoints(geometry) < 300
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AND subclass IN ('wood', 'forest')) union_geom300
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GROUP BY subclass,
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cid
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@ -129,26 +101,12 @@ CREATE INDEX ON simplify_vw_z11 USING GIST (geometry);
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-- etldoc: simplify_vw_z11 -> osm_landcover_gen_z11
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CREATE TABLE osm_landcover_gen_z11 AS
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(
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SELECT subclass,
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ST_MakeValid(
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(ST_dump(
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ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z11
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WHERE ST_NPoints(geometry) < 50
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AND subclass IN ('wood', 'forest')) union_geom50
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GROUP BY subclass,
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cid
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UNION ALL
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SELECT subclass, ST_MakeValid((ST_dump(ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z11
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WHERE ST_NPoints(geometry) >= 50
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AND ST_NPoints(geometry) < 300
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WHERE ST_NPoints(geometry) < 300
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AND subclass IN ('wood', 'forest')) union_geom300
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GROUP BY subclass,
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cid
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@ -179,26 +137,12 @@ CREATE INDEX ON simplify_vw_z10 USING GIST (geometry);
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-- etldoc: simplify_vw_z10 -> osm_landcover_gen_z10
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CREATE TABLE osm_landcover_gen_z10 AS
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(
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SELECT subclass,
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ST_MakeValid(
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(ST_dump(
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ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z10
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WHERE ST_NPoints(geometry) < 50
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AND subclass IN ('wood', 'forest')) union_geom50
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GROUP BY subclass,
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cid
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UNION ALL
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SELECT subclass, ST_MakeValid((ST_dump(ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z10
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WHERE ST_NPoints(geometry) >= 50
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AND ST_NPoints(geometry) < 300
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WHERE ST_NPoints(geometry) < 300
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AND subclass IN ('wood', 'forest')) union_geom300
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GROUP BY subclass,
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cid
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@ -229,26 +173,12 @@ CREATE INDEX ON simplify_vw_z9 USING GIST (geometry);
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-- etldoc: simplify_vw_z9 -> osm_landcover_gen_z9
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CREATE TABLE osm_landcover_gen_z9 AS
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(
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SELECT subclass,
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ST_MakeValid(
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(ST_dump(
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ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z9
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WHERE ST_NPoints(geometry) < 50
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AND subclass IN ('wood', 'forest')) union_geom50
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GROUP BY subclass,
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cid
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UNION ALL
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SELECT subclass, ST_MakeValid((ST_dump(ST_Union(geometry))).geom) AS geometry
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FROM (
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SELECT subclass,
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ST_ClusterDBSCAN(geometry, eps := 0, minpoints := 1) over () AS cid, geometry
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FROM simplify_vw_z9
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WHERE ST_NPoints(geometry) >= 50
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AND ST_NPoints(geometry) < 300
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WHERE ST_NPoints(geometry) < 300
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AND subclass IN ('wood', 'forest')) union_geom300
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GROUP BY subclass,
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cid
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