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Adjust overview clustered point to pixel centers

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Fixes #240
This commit is contained in:
Javier Goizueta
2016-04-23 15:07:06 +02:00
parent 897689dd43
commit 580ec38ab8
1 changed files with 12 additions and 3 deletions
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15
scripts-available/CDB_Overviews.sql
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@@ -652,7 +652,9 @@ AS $$
overview_rel TEXT;
reduction FLOAT8;
base_name TEXT;
pixel_m FLOAT8;
grid_m FLOAT8;
offset_m FLOAT8;
aggr_attributes TEXT;
attributes TEXT;
columns TEXT;
@@ -678,8 +680,10 @@ AS $$
SELECT * FROM _cdb_split_table_name(reloid) INTO schema_name, table_name;
-- compute grid cell size using the overview_z dimension...
SELECT CDB_XYZ_Resolution(overview_z)*grid_px INTO grid_m;
-- pixel_m: size of a pixel in webmercator units (meters)
SELECT CDB_XYZ_Resolution(overview_z) INTO pixel_m;
-- grid size in meters
grid_m = grid_px * pixel_m;
attributes := _CDB_Aggregable_Attributes_Expression(reloid);
aggr_attributes := _CDB_Aggregated_Attributes_Expression(reloid);
@@ -690,7 +694,12 @@ AS $$
aggr_attributes := aggr_attributes || ', ';
END IF;
point_geom = Format('ST_SetSRID(ST_MakePoint(gx*%1$s + %2$s, gy*%1$s + %2$s), 3857)', grid_m, grid_m/2);
-- points are displaced to it's cell's center
offset_m := grid_m/2;
-- then corrected to be at the nearest pixel's center (by up to half a pixel)
offset_m := offset_m + pixel_m/2 - MOD((grid_m/2)::numeric, pixel_m::numeric)::float8;
point_geom := Format('ST_SetSRID(ST_MakePoint(gx*%1$s + %2$s, gy*%1$s + %2$s), 3857)', grid_m, offset_m);
-- compute the resulting columns in the same order as in the base table
WITH cols AS (