sql

lib/sql/test/CDB_HexagonTest.sql

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+set client_min_messages to error;
+\set VERBOSITY TERSE
+
+-- Check correctness of an hexagons grid
+--
+-- Cells must have no overlaps and have a number of
+-- intersections with other cells between 2 and 6
+--
+
+WITH
+ params AS ( SELECT ST_MakeEnvelope(10, 10, 20, 20) as env, 2 as radius ),
+ grid AS ( SELECT CDB_HexagonGrid(env, radius) AS cell from params),
+ igrid AS ( SELECT row_number() over (), cell from grid )
+
+ SELECT count(row_number) as r1, sum(st_npoints(cell)) as r2, 'count / npoints' as err
+ FROM igrid g1
+
+UNION ALL
+
+ SELECT g1.row_number as r1, g2.row_number as r2, 'overlap' as err
+ FROM igrid g1, igrid g2
+ WHERE g2.row_number > g1.row_number AND
+       ST_Overlaps(g1.cell, g2.cell)
+
+UNION ALL
+
+ SELECT g1.row_number, count(g2.row_number) as r2, 'n intersections' as err
+ FROM igrid g1, igrid g2
+ WHERE g1.row_number != g2.row_number AND
+       ST_Intersects(g1.cell, g2.cell)
+       GROUP BY g1.row_number
+       HAVING count(g2.row_number) > 6 OR count(g2.row_number) < 2
+
+UNION ALL
+
+ SELECT g1.row_number, null::integer, 'centroid out of extent' as err
+ FROM igrid g1, params
+ WHERE NOT ST_Intersects(ST_Centroid(g1.cell), params.env)
+
+	;
+
+
+-- Check robustness of HexagonGrid generation
+
+WITH
+ params AS ( SELECT
+ ST_MakeEnvelope(-20037508.5,20037507,-20037508,20037507.5) as env,
+ 0.002 as radius ),
+ grid AS ( SELECT CDB_HexagonGrid(env, radius) AS cell from params)
+SELECT '#160', count(cell) > 23000 from grid;
+
+-- Check small grids are generated...
+SELECT COUNT(*) FROM cartodb.CDB_HexagonGrid(ST_MakeEnvelope(0,0,1000,1000,3857), 10);
+
+-- But large grids produce an error
+SELECT COUNT(*) FROM cartodb.CDB_HexagonGrid(ST_MakeEnvelope(0,0,1000,1000,3857), 1);