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7ea4289 Feb 14, 2018
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@jgoizueta @Algunenano
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-- Return an Hexagon with given center and side (or maximal radius)
CREATE OR REPLACE FUNCTION CDB_MakeHexagon(center GEOMETRY, radius FLOAT8)
RETURNS GEOMETRY
AS $$
SELECT ST_MakePolygon(ST_MakeLine(geom))
FROM
(
SELECT (ST_DumpPoints(ST_ExteriorRing(ST_Buffer($1, $2, 3)))).*
) as points
WHERE path[1] % 2 != 0
$$ LANGUAGE 'sql' IMMUTABLE STRICT PARALLEL SAFE;
-- In older versions of the extension, CDB_HexagonGrid had a different signature
DROP FUNCTION IF EXISTS cartodb.CDB_HexagonGrid(GEOMETRY, FLOAT8, GEOMETRY);
--
-- Fill given extent with an hexagonal coverage
--
-- @param ext Extent to fill. Only hexagons with center point falling
-- inside the extent (or at the lower or leftmost edge) will
-- be emitted. The returned hexagons will have the same SRID
-- as this extent.
--
-- @param side Side measure for the hexagon.
-- Maximum diameter will be 2 * side.
--
-- @param origin Optional origin to allow for exact tiling.
-- If omitted the origin will be 0,0.
-- The parameter is checked for having the same SRID
-- as the extent.
--
-- @param maxcells Optional maximum number of grid cells to generate;
-- if the grid requires more cells to cover the extent
-- and exception will occur.
----
-- DROP FUNCTION IF EXISTS CDB_HexagonGrid(ext GEOMETRY, side FLOAT8);
CREATE OR REPLACE FUNCTION CDB_HexagonGrid(ext GEOMETRY, side FLOAT8, origin GEOMETRY DEFAULT NULL, maxcells INTEGER DEFAULT 512*512)
RETURNS SETOF GEOMETRY
AS $$
DECLARE
h GEOMETRY; -- hexagon
c GEOMETRY; -- center point
rec RECORD;
hstep FLOAT8; -- horizontal step
vstep FLOAT8; -- vertical step
vstart FLOAT8;
vstartary FLOAT8[];
vstartidx INTEGER;
hskip BIGINT;
hstart FLOAT8;
hend FLOAT8;
vend FLOAT8;
xoff FLOAT8;
yoff FLOAT8;
xgrd FLOAT8;
ygrd FLOAT8;
srid INTEGER;
BEGIN
-- | |
-- |hstep|
-- ______ ___ |
-- vstep / \ ___ /
-- ______ \ ___ / \
-- / \ ___ /
--
--
RAISE DEBUG 'Side: %', side;
vstep := side * sqrt(3); -- x 2 ?
hstep := side * 1.5;
RAISE DEBUG 'vstep: %', vstep;
RAISE DEBUG 'hstep: %', hstep;
srid := ST_SRID(ext);
xoff := 0;
yoff := 0;
IF origin IS NOT NULL THEN
IF ST_SRID(origin) != srid THEN
RAISE EXCEPTION 'SRID mismatch between extent (%) and origin (%)', srid, ST_SRID(origin);
END IF;
xoff := ST_X(origin);
yoff := ST_Y(origin);
END IF;
RAISE DEBUG 'X offset: %', xoff;
RAISE DEBUG 'Y offset: %', yoff;
xgrd := side * 0.5;
ygrd := ( side * sqrt(3) ) / 2.0;
RAISE DEBUG 'X grid size: %', xgrd;
RAISE DEBUG 'Y grid size: %', ygrd;
-- Tweak horizontal start on hstep*2 grid from origin
hskip := ceil((ST_XMin(ext)-xoff)/hstep);
RAISE DEBUG 'hskip: %', hskip;
hstart := xoff + hskip*hstep;
RAISE DEBUG 'hstart: %', hstart;
-- Tweak vertical start on hstep grid from origin
vstart := yoff + ceil((ST_Ymin(ext)-yoff)/vstep)*vstep;
RAISE DEBUG 'vstart: %', vstart;
hend := ST_XMax(ext);
vend := ST_YMax(ext);
IF vstart - (vstep/2.0) < ST_YMin(ext) THEN
vstartary := ARRAY[ vstart + (vstep/2.0), vstart ];
ELSE
vstartary := ARRAY[ vstart - (vstep/2.0), vstart ];
END IF;
If maxcells IS NOT NULL AND maxcells > 0 THEN
IF CEIL((CEIL((vend-vstart)/(vstep/2.0)) * CEIL((hend-hstart)/(hstep*2.0/3.0)))/3.0)::integer > maxcells THEN
RAISE EXCEPTION 'The requested grid is too big to be rendered';
END IF;
END IF;
vstartidx := abs(hskip)%2;
RAISE DEBUG 'vstartary: % : %', vstartary[1], vstartary[2];
RAISE DEBUG 'vstartidx: %', vstartidx;
c := ST_SetSRID(ST_MakePoint(hstart, vstartary[vstartidx+1]), srid);
h := ST_SnapToGrid(CDB_MakeHexagon(c, side), xoff, yoff, xgrd, ygrd);
vstartidx := (vstartidx + 1) % 2;
WHILE ST_X(c) < hend LOOP -- over X
--RAISE DEBUG 'X loop starts, center point: %', ST_AsText(c);
WHILE ST_Y(c) < vend LOOP -- over Y
--RAISE DEBUG 'Center: %', ST_AsText(c);
--h := ST_SnapToGrid(CDB_MakeHexagon(c, side), xoff, yoff, xgrd, ygrd);
RETURN NEXT h;
h := ST_SnapToGrid(ST_Translate(h, 0, vstep), xoff, yoff, xgrd, ygrd);
c := ST_Translate(c, 0, vstep); -- TODO: drop ?
END LOOP;
-- TODO: translate h direcly ...
c := ST_SetSRID(ST_MakePoint(ST_X(c)+hstep, vstartary[vstartidx+1]), srid);
h := ST_SnapToGrid(CDB_MakeHexagon(c, side), xoff, yoff, xgrd, ygrd);
vstartidx := (vstartidx + 1) % 2;
END LOOP;
RETURN;
END
$$ LANGUAGE 'plpgsql' IMMUTABLE PARALLEL SAFE;