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Optimize the gridded clustering strategy

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The internal grid_px parameter is adjusted for best results with default symbol size
This commit is contained in:
Javier Goizueta 2015-12-22 17:59:49 +01:00
parent c8a1ef6f68
commit 5a78ee2896
1 changed files with 18 additions and 14 deletions
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32
scripts-available/CDB_Overviews.sql
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@ -175,7 +175,7 @@ AS $$
overview_rel TEXT;
reduction FLOAT8;
base_name TEXT;
grid_px FLOAT8 = 3.0;
grid_px FLOAT8 = 7.5; -- Grid size in pixels at Z level overview_z
grid_m FLOAT8;
aggr_attributes TEXT;
attributes TEXT;
@ -193,27 +193,31 @@ AS $$
aggr_attributes := '';
EXECUTE Format('DROP TABLE IF EXISTS %s CASCADE;', overview_rel);
-- Now we cluster the data using a grid of size grid_m
-- and selecte the centroid (average coordinates) of each cluster.
-- If we had a selected numeric attribute of interest we could use it
-- as a weight for the average coordinates.
EXECUTE Format('
CREATE TABLE %3$s AS
WITH clusters AS (
SELECT
first_value(f.cartodb_id) OVER (
PARTITION BY
Floor(ST_X(f.the_geom_webmercator)/%2$s)::int,
Floor(ST_Y(f.the_geom_webmercator)/%2$s)::int
) AS cartodb_id,
%4$s
the_geom,
the_geom_webmercator
FROM %1$s f
%5$s
count(*) AS n,
SUM(ST_X(f.the_geom_webmercator)) AS sx,
SUM(ST_Y(f.the_geom_webmercator)) AS sy,
Floor(ST_X(f.the_geom_webmercator)/%2$s)::int AS gx,
Floor(ST_Y(f.the_geom_webmercator)/%2$s)::int AS gy,
row_number() OVER () AS cartodb_id
FROM %1$s f
GROUP BY gx, gy
)
SELECT
%4$s
cartodb_id,
ST_Centroid(ST_Collect(clusters.the_geom)) AS the_geom,
%5$s
ST_Centroid(ST_Collect(clusters.the_geom_webmercator)) AS the_geom_webmercator
ST_SetSRID(ST_MakePoint(sx/n, sy/n), 3857) AS the_geom_webmercator,
ST_Transform(ST_SetSRID(ST_MakePoint(sx/n, sy/n), 3857), 4326) AS the_geom
FROM clusters
GROUP BY cartodb_id;
', reloid::text, grid_m, overview_rel, attributes, aggr_attributes);
RETURN overview_rel;