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.

Warning

• 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

Warning

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.

Warning

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

• Source code