H2GIS

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ST_MakeValid

Signatures

GEOMETRY ST_MakeValid(GEOMETRY geom);
GEOMETRY ST_MakeValid(GEOMETRY geom, 
                      BOOLEAN preserveGeomDim);
GEOMETRY ST_MakeValid(GEOMETRY geom, 
                      BOOLEAN preserveGeomDim, 
                      BOOLEAN preserveDuplicateCoord);
GEOMETRY ST_MakeValid(GEOMETRY geom, 
                      BOOLEAN preserveGeomDim, 
                      BOOLEAN preserveDuplicateCoord, 
                      BOOLEAN preserveCoordDim);

Description

Repair an invalid geometry.

Here, geometry can be (multi)point, (multi)linestring, (multi)polygon or geometryCollection.

Parameter: preserveGeomDim
Value Description Default value
true Remove degenerated geometries from the result, i.e geometries which dimension is lower than the input geometry x
false It is up to the client to filter degenerate geometries  

Note that:

  • A multi-geometry will always produce a multi-geometry (eventually empty or made of a single component).
  • A simple geometry may produce a multi-geometry (i.e polygon with self-intersection will generally produce a multi-polygon). In this case, it is up to the client to explode multi-geometries if needed.

- Linear geometries (dim = 1): duplicate coordinates are preserved as much as possible.
- Aeral geometries (dim = 2): duplicate coordinates are generally removed due to the use of overlay operations.

Parameter: preserveDuplicateCoord
Value Description Default value
true Preserve duplicate coordinates as much as possible. Generally, duplicate coordinates can be preserved for linear geometries but not for areal geometries (overlay operations used to repair polygons remove duplicate points) x
false All duplicated coordinates are removed  
Parameter: preserveCoordDim
Value Description Default value
true Preserves third and fourth ordinates x
false Preserves third ordinates but not fourth one  

Note that the fourth dimension is not yet supported in H2GIS. So for the moment, preserveCoordDim has no impact since third ordinates (z) will always be preserved.

ST_MakeValid may add new points to node the original set of lines (especially to make polygons valid). New points just have x and y. No interpolation is performed if original geometry is in 3D or 4D.

Examples

With Point
SELECT ST_MakeValid('POINT(0 0)');
-- Answer: POINT(0 0) 

-- Also works with z coordinates
SELECT ST_MakeValid('POINT(1 2 3)');
-- Answer: POINT(1 2 3)
With Linestring
SELECT ST_MakeValid('
           LINESTRING(0 0, 10 0, 20 0, 20 0, 30 0)');
-- Answer: LINESTRING(0 0, 10 0, 20 0, 20 0, 30 0) 

-- Same example but with preserveDuplicateCoord = false. 
-- So here duplicated coordinates are removed
SELECT ST_MakeValid('
           LINESTRING(0 0, 10 0, 20 0, 20 0, 30 0)', true, false);
-- Answer: LINESTRING(0 0, 10 0, 20 0, 30 0) 

-- Same example but with z coordinates
SELECT ST_MakeValid('
           LINESTRING(0 0 1, 10 0 2, 20 0 1, 20 0 1, 30 0 1)', 
           true,false);
-- Answer: LINESTRING(0 0 1, 10 0 2, 20 0 1, 30 0 1)

-- --------------------------------------------------------
-- Example with 'preserveGeomDim'
-- True
SELECT ST_MakeValid('
           LINESTRING(1 1, 1 1)', true);
-- Answer: LINESTRING EMPTY 

-- False
SELECT ST_MakeValid('
           LINESTRING(1 1, 1 1)', false);
-- Answer: POINT (1 1)
With Polygon
SELECT ST_MakeValid('
           POLYGON((1 5, 1 1, 3 3, 5 3, 7 1, 7 5, 5 3, 3 3, 1 5))');
-- Answer: MULTIPOLYGON(((3 3, 1 1, 1 5, 3 3)), 
--                      ((5 3, 7 5, 7 1, 5 3))) 

SELECT ST_MakeValid('
           MULTIPOLYGON(((0 0, 3 0, 3 3, 0 3, 0 0)), 
                        ((3 0, 6 0, 6 3, 3 3, 3 0)))', false);
-- Answer: MULTIPOLYGON(((3 0, 0 0, 0 3, 3 3, 6 3, 6 0, 3 0))) 

SELECT ST_MakeValid('
           POLYGON ((1 1, 1 3, 3 3, 3 2, 2 2, 3 2, 3 1, 1 1))');
-- Answer: POLYGON((3 2, 3 1, 1 1, 1 3, 3 3, 3 2)) 

SELECT ST_MakeValid('
           POLYGON ((1 1, 3 1, 0 2, 3 3, 1 3, 1 1))');
-- Answer: MULTIPOLYGON(
--         ((1 2.33, 1 1.66, 0 2, 1 2.33)), 
--         ((1 1.66, 3 1, 1 1, 1 1.66)), 
--         ((1 2.33, 1 3, 3 3, 1 2.33))) 

-- Same example but with z coordinates. 
-- Here, created nodes have no z information.
SELECT ST_MakeValid('
           POLYGON ((1 1 0, 3 1 1, 0 2 1, 3 3 0, 1 3 1, 1 1 0))');
-- Answer: MULTIPOLYGON (
--         ((1 2.33, 1 1.66, 0 2 1, 1 2.33)), 
--         ((1 1.66, 3 1 1, 1 1 0, 1 1.66)), 
--         ((1 2.33, 1 3 1, 3 3 0, 1 2.33))) 

SELECT ST_MakeValid('
           POLYGON((1 1, 1 4, 6 4, 4 4, 1 1))');
-- Answer: POLYGON((4 4, 1 1, 1 4, 4 4))

SELECT ST_MakeValid('
           MULTIPOLYGON(((1 1, 1 3, 2 2, 0 2, 1 1)), 
                        ((3 3, 3 1, 4 1, 5 3, 4 3, 5 3, 3 3)))');
-- Answer: MULTIPOLYGON(((1 2, 1 1, 0 2, 1 2)), 
--                      ((1 2, 1 3, 2 2, 1 2)), 
--                      ((5 3, 4 1, 3 1, 3 3, 4 3, 5 3)))

With GeometryCollection
SELECT ST_MakeValid('
    GEOMETRYCOLLECTION (
           POLYGON ((1 1, 1 1, 1 3, 2 2, 0 2, 1 1)), 
           LINESTRING (3 1, 3 3, 3 3, 4 3), 
           POINT (5 2))');
-- Answer: GEOMETRYCOLLECTION (
--         POLYGON ((1 2, 1 1, 0 2, 1 2)), 
--         POLYGON ((1 2, 1 3, 2 2, 1 2)), 
--         LINESTRING (3 1, 3 3, 3 3, 4 3), 
--         POINT (5 2)) 

-- Same example but with preserveDuplicateCoord = false
SELECT ST_MakeValid('
    GEOMETRYCOLLECTION (
           POLYGON ((1 1, 1 1, 1 3, 2 2, 0 2, 1 1)), 
           LINESTRING (3 1, 3 3, 3 3, 4 3), 
           POINT (5 2))', true, false);
-- Answer: GEOMETRYCOLLECTION (
--         POLYGON ((1 2, 1 1, 0 2, 1 2)), 
--         POLYGON ((1 2, 1 3, 2 2, 1 2)), 
--         LINESTRING (3 1, 3 3, 4 3), 
--         POINT (5 2))

See also