0082138503
We'll bet on no old signature being left around. Presence of an old signature would break at runtime with a message like: ERROR: function CDB_UserTables() is not unique Closes #25
136 lines
3.9 KiB
PL/PgSQL
136 lines
3.9 KiB
PL/PgSQL
-- Return an Hexagon with given center and side (or maximal radius)
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CREATE OR REPLACE FUNCTION CDB_MakeHexagon(center GEOMETRY, radius FLOAT8)
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RETURNS GEOMETRY
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AS $$
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SELECT ST_MakePolygon(ST_MakeLine(geom))
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FROM
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(
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SELECT (ST_DumpPoints(ST_ExteriorRing(ST_Buffer($1, $2, 3)))).*
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) as points
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WHERE path[1] % 2 != 0
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$$ LANGUAGE 'sql' IMMUTABLE STRICT;
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--
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-- Fill given extent with an hexagonal coverage
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--
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-- @param ext Extent to fill. Only hexagons with center point falling
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-- inside the extent (or at the lower or leftmost edge) will
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-- be emitted. The returned hexagons will have the same SRID
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-- as this extent.
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--
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-- @param side Side measure for the hexagon.
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-- Maximum diameter will be 2 * side.
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--
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-- @param origin Optional origin to allow for exact tiling.
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-- If omitted the origin will be 0,0.
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-- The parameter is checked for having the same SRID
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-- as the extent.
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--
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--
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-- DROP FUNCTION IF EXISTS CDB_HexagonGrid(ext GEOMETRY, side FLOAT8);
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CREATE OR REPLACE FUNCTION CDB_HexagonGrid(ext GEOMETRY, side FLOAT8, origin GEOMETRY DEFAULT NULL)
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RETURNS SETOF GEOMETRY
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AS $$
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DECLARE
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h GEOMETRY; -- hexagon
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c GEOMETRY; -- center point
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rec RECORD;
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hstep FLOAT8; -- horizontal step
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vstep FLOAT8; -- vertical step
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vstart FLOAT8;
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vstartary FLOAT8[];
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vstartidx INTEGER;
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hskip BIGINT;
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hstart FLOAT8;
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hend FLOAT8;
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vend FLOAT8;
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xoff FLOAT8;
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yoff FLOAT8;
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xgrd FLOAT8;
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ygrd FLOAT8;
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srid INTEGER;
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BEGIN
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-- | |
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-- |hstep|
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-- ______ ___ |
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-- vstep / \ ___ /
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-- ______ \ ___ / \
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-- / \ ___ /
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--
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--
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RAISE DEBUG 'Side: %', side;
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vstep := side * sqrt(3); -- x 2 ?
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hstep := side * 1.5;
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RAISE DEBUG 'vstep: %', vstep;
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RAISE DEBUG 'hstep: %', hstep;
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srid := ST_SRID(ext);
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xoff := 0;
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yoff := 0;
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IF origin IS NOT NULL THEN
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IF ST_SRID(origin) != srid THEN
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RAISE EXCEPTION 'SRID mismatch between extent (%) and origin (%)', srid, ST_SRID(origin);
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END IF;
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xoff := ST_X(origin);
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yoff := ST_Y(origin);
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END IF;
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RAISE DEBUG 'X offset: %', xoff;
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RAISE DEBUG 'Y offset: %', yoff;
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xgrd := side * 0.5;
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ygrd := ( side * sqrt(3) ) / 2.0;
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RAISE DEBUG 'X grid size: %', xgrd;
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RAISE DEBUG 'Y grid size: %', ygrd;
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-- Tweak horizontal start on hstep*2 grid from origin
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hskip := ceil((ST_XMin(ext)-xoff)/hstep);
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RAISE DEBUG 'hskip: %', hskip;
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hstart := xoff + hskip*hstep;
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RAISE DEBUG 'hstart: %', hstart;
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-- Tweak vertical start on hstep grid from origin
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vstart := yoff + ceil((ST_Ymin(ext)-yoff)/vstep)*vstep;
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RAISE DEBUG 'vstart: %', vstart;
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hend := ST_XMax(ext);
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vend := ST_YMax(ext);
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IF vstart - (vstep/2.0) < ST_YMin(ext) THEN
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vstartary := ARRAY[ vstart + (vstep/2.0), vstart ];
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ELSE
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vstartary := ARRAY[ vstart - (vstep/2.0), vstart ];
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END IF;
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vstartidx := abs(hskip)%2;
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RAISE DEBUG 'vstartary: % : %', vstartary[1], vstartary[2];
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RAISE DEBUG 'vstartidx: %', vstartidx;
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c := ST_SetSRID(ST_MakePoint(hstart, vstartary[vstartidx+1]), srid);
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h := ST_SnapToGrid(CDB_MakeHexagon(c, side), xoff, yoff, xgrd, ygrd);
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vstartidx := (vstartidx + 1) % 2;
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WHILE ST_X(c) < hend LOOP -- over X
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--RAISE DEBUG 'X loop starts, center point: %', ST_AsText(c);
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WHILE ST_Y(c) < vend LOOP -- over Y
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--RAISE DEBUG 'Center: %', ST_AsText(c);
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--h := ST_SnapToGrid(CDB_MakeHexagon(c, side), xoff, yoff, xgrd, ygrd);
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RETURN NEXT h;
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h := ST_SnapToGrid(ST_Translate(h, 0, vstep), xoff, yoff, xgrd, ygrd);
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c := ST_Translate(c, 0, vstep); -- TODO: drop ?
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END LOOP;
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-- TODO: translate h direcly ...
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c := ST_SetSRID(ST_MakePoint(ST_X(c)+hstep, vstartary[vstartidx+1]), srid);
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h := ST_SnapToGrid(CDB_MakeHexagon(c, side), xoff, yoff, xgrd, ygrd);
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vstartidx := (vstartidx + 1) % 2;
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END LOOP;
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RETURN;
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END
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$$ LANGUAGE 'plpgsql' IMMUTABLE;
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