These functions test whether geometries are valid according to the OGC SFS standard. They also provide information about the nature and location of invalidity. There is also a function to create a valid geometry out of an invalid one.

# Geometry Validation

ST_IsValid

Tests if a geometry is well-formed in 2D.

    			boolean ST_IsValid

    			geometry  g

    			boolean ST_IsValid

    			geometry  g
    			integer  flags

### Description

Tests if an ST_Geometry value is well-formed and valid in 2D according to the OGC rules. For geometries with 3 and 4 dimensions, the validity is still only tested in 2 dimensions. For geometries that are invalid, a PostgreSQL NOTICE is emitted providing details of why it is not valid.

For the version with the `flags` parameter, supported values are documented in ST_IsValidDetail This version does not print a NOTICE explaining invalidity.

For more information on the definition of geometry validity, refer to OGC_Validity

SQL-MM defines the result of ST_IsValid(NULL) to be 0, while PostGIS returns NULL.

Performed by the GEOS module.

The version accepting flags is available starting with 2.0.0.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 5.1.9

Neither OGC-SFS nor SQL-MM specifications include a flag argument for ST_IsValid. The flag is a PostGIS extension.

### Examples

    SELECT ST_IsValid(ST_GeomFromText('LINESTRING(0 0, 1 1)')) As good_line,
    	ST_IsValid(ST_GeomFromText('POLYGON((0 0, 1 1, 1 2, 1 1, 0 0))')) As bad_poly
    --results
    NOTICE:  Self-intersection at or near point 0 0
     good_line | bad_poly
    -----------+----------
     t         | f

### See Also

ST_IsSimple, ST_IsValidReason, ST_IsValidDetail,

ST_IsValidDetail

Returns a `valid_detail` row stating if a geometry is valid or if not a reason and a location.

    			valid_detail ST_IsValidDetail
    			geometry  geom
    			integer  flags

### Description

Returns a `valid_detail` row, containing a boolean (`valid`) stating if a geometry is valid, a varchar (`reason`) stating a reason why it is invalid and a geometry (`location`) pointing out where it is invalid.

Useful to improve on the combination of ST_IsValid and ST_IsValidReason to generate a detailed report of invalid geometries.

The optional `flags` parameter is a bitfield. It can have the following values:

- 0: Use usual OGC SFS validity semantics.

- 1: Consider certain kinds of self-touching rings (inverted shells and exverted holes) as valid. This is also known as "the ESRI flag", since this is the validity model used by those tools. Note that this is invalid under the OGC model.

Performed by the GEOS module.

Availability: 2.0.0

### Examples

    --First 3 Rejects from a successful quintuplet experiment
    SELECT gid, reason(ST_IsValidDetail(geom)), ST_AsText(location(ST_IsValidDetail(geom))) as location
    FROM
    (SELECT ST_MakePolygon(ST_ExteriorRing(e.buff), array_agg(f.line)) As geom, gid
    FROM (SELECT ST_Buffer(ST_Point(x1*10,y1), z1) As buff, x1*10 + y1*100 + z1*1000 As gid
    	FROM generate_series(-4,6) x1
    	CROSS JOIN generate_series(2,5) y1
    	CROSS JOIN generate_series(1,8) z1
    	WHERE x1 > y1*0.5 AND z1 < x1*y1) As e
    	INNER JOIN (SELECT ST_Translate(ST_ExteriorRing(ST_Buffer(ST_Point(x1*10,y1), z1)),y1*1, z1*2) As line
    	FROM generate_series(-3,6) x1
    	CROSS JOIN generate_series(2,5) y1
    	CROSS JOIN generate_series(1,10) z1
    	WHERE x1 > y1*0.75 AND z1 < x1*y1) As f
    ON (ST_Area(e.buff) > 78 AND ST_Contains(e.buff, f.line))
    GROUP BY gid, e.buff) As quintuplet_experiment
    WHERE ST_IsValid(geom) = false
    ORDER BY gid
    LIMIT 3;

     gid  |      reason       |  location
    ------+-------------------+-------------
     5330 | Self-intersection | POINT(32 5)
     5340 | Self-intersection | POINT(42 5)
     5350 | Self-intersection | POINT(52 5)

     --simple example
    SELECT * FROM ST_IsValidDetail('LINESTRING(220227 150406,2220227 150407,222020 150410)');

     valid | reason | location
    -------+--------+----------
     t     |        |

### See Also

ST_IsValid, ST_IsValidReason

ST_IsValidReason

Returns text stating if a geometry is valid, or a reason for invalidity.

    			text ST_IsValidReason
    			geometry  geomA

    			text ST_IsValidReason
    			geometry  geomA
    			integer  flags

### Description

Returns text stating if a geometry is valid, or if invalid a reason why.

Useful in combination with ST_IsValid to generate a detailed report of invalid geometries and reasons.

Allowed `flags` are documented in ST_IsValidDetail.

Performed by the GEOS module.

Availability: 1.4

Availability: 2.0 version taking flags.

### Examples

    -- invalid bow-tie polygon
    SELECT ST_IsValidReason(
        'POLYGON ((100 200, 100 100, 200 200,
         200 100, 100 200))'::geometry) as validity_info;
    validity_info
    --------------------------
    Self-intersection[150 150]

    --First 3 Rejects from a successful quintuplet experiment
    SELECT gid, ST_IsValidReason(geom) as validity_info
    FROM
    (SELECT ST_MakePolygon(ST_ExteriorRing(e.buff), array_agg(f.line)) As geom, gid
    FROM (SELECT ST_Buffer(ST_Point(x1*10,y1), z1) As buff, x1*10 + y1*100 + z1*1000 As gid
    	FROM generate_series(-4,6) x1
    	CROSS JOIN generate_series(2,5) y1
    	CROSS JOIN generate_series(1,8) z1
    	WHERE x1 > y1*0.5 AND z1 < x1*y1) As e
    	INNER JOIN (SELECT ST_Translate(ST_ExteriorRing(ST_Buffer(ST_Point(x1*10,y1), z1)),y1*1, z1*2) As line
    	FROM generate_series(-3,6) x1
    	CROSS JOIN generate_series(2,5) y1
    	CROSS JOIN generate_series(1,10) z1
    	WHERE x1 > y1*0.75 AND z1 < x1*y1) As f
    ON (ST_Area(e.buff) > 78 AND ST_Contains(e.buff, f.line))
    GROUP BY gid, e.buff) As quintuplet_experiment
    WHERE ST_IsValid(geom) = false
    ORDER BY gid
    LIMIT 3;

     gid  |      validity_info
    ------+--------------------------
     5330 | Self-intersection [32 5]
     5340 | Self-intersection [42 5]
     5350 | Self-intersection [52 5]

     --simple example
    SELECT ST_IsValidReason('LINESTRING(220227 150406,2220227 150407,222020 150410)');

     st_isvalidreason
    ------------------
     Valid Geometry

### See Also

ST_IsValid, ST_Summary

ST_MakeValid

Attempts to make an invalid geometry valid without losing vertices.

                geometry ST_MakeValid
                geometry input

                geometry ST_MakeValid
                geometry input
                text params

### Description

The function attempts to create a valid representation of a given invalid geometry without losing any of the input vertices. Valid geometries are returned unchanged.

Supported inputs are: POINTS, MULTIPOINTS, LINESTRINGS, MULTILINESTRINGS, POLYGONS, MULTIPOLYGONS and GEOMETRYCOLLECTIONS containing any mix of them.

In case of full or partial dimensional collapses, the output geometry may be a collection of lower-to-equal dimension geometries, or a geometry of lower dimension.

Single polygons may become multi-geometries in case of self-intersections.

The `params` argument can be used to supply an options string to select the method to use for building valid geometry. The options string is in the format "method=linework|structure keepcollapsed=true|false".

The "method" key has two values.

- "linework" is the original algorithm, and builds valid geometries by first extracting all lines, noding that linework together, then building a value output from the linework.

- "structure" is an algorithm that distinguishes between interior and exterior rings, building new geometry by unioning exterior rings, and then differencing all interior rings.

The "keepcollapsed" key is only valid for the "structure" algorithm, and takes a value of "true" or "false". When set to "false", geometry components that collapse to a lower dimensionality, for example a one-point linestring would be dropped.

Performed by the GEOS module.

Availability: 2.0.0

Enhanced: 2.0.1, speed improvements

Enhanced: 2.1.0, added support for GEOMETRYCOLLECTION and MULTIPOINT.

Enhanced: 3.1.0, added removal of Coordinates with NaN values.

Enhanced: 3.2.0, added algorithm options, 'linework' and 'structure'.

&Z_support;

### Examples

before_geom: MULTIPOLYGON of 2 overlapping polygons after_geom: MULTIPOLYGON of 4 non-overlapping polygons after_geom_structure: MULTIPOLYGON of 1 non-overlapping polygon
    SELECT f.geom AS before_geom, ST_MakeValid(f.geom) AS after_geom, ST_MakeValid(f.geom, 'method=structure') AS after_geom_structure
    FROM (SELECT 'MULTIPOLYGON(((186 194,187 194,188 195,189 195,190 195,
    191 195,192 195,193 194,194 194,194 193,195 192,195 191,
    195 190,195 189,195 188,194 187,194 186,14 6,13 6,12 5,11 5,
    10 5,9 5,8 5,7 6,6 6,6 7,5 8,5 9,5 10,5 11,5 12,6 13,6 14,186 194)),
    ((150 90,149 80,146 71,142 62,135 55,128 48,119 44,110 41,100 40,
    90 41,81 44,72 48,65 55,58 62,54 71,51 80,50 90,51 100,
    54 109,58 118,65 125,72 132,81 136,90 139,100 140,110 139,
    119 136,128 132,135 125,142 118,146 109,149 100,150 90)))'::geometry AS geom) AS f;
before_geom: MULTIPOLYGON of 6 overlapping polygons after_geom: MULTIPOLYGON of 14 Non-overlapping polygons after_geom_structure: MULTIPOLYGON of 1 Non-overlapping polygon
    SELECT c.geom AS before_geom,
                        ST_MakeValid(c.geom) AS after_geom,
                        ST_MakeValid(c.geom, 'method=structure') AS after_geom_structure
    	FROM (SELECT 'MULTIPOLYGON(((91 50,79 22,51 10,23 22,11 50,23 78,51 90,79 78,91 50)),
    		  ((91 100,79 72,51 60,23 72,11 100,23 128,51 140,79 128,91 100)),
    		  ((91 150,79 122,51 110,23 122,11 150,23 178,51 190,79 178,91 150)),
    		  ((141 50,129 22,101 10,73 22,61 50,73 78,101 90,129 78,141 50)),
    		  ((141 100,129 72,101 60,73 72,61 100,73 128,101 140,129 128,141 100)),
    		  ((141 150,129 122,101 110,73 122,61 150,73 178,101 190,129 178,141 150)))'::geometry AS geom) AS c;

### Examples

    SELECT ST_AsText(ST_MakeValid(
        'LINESTRING(0 0, 0 0)',
        'method=structure keepcollapsed=true'
        ));

     st_astext
    ------------
     POINT(0 0)

    SELECT ST_AsText(ST_MakeValid(
        'LINESTRING(0 0, 0 0)',
        'method=structure keepcollapsed=false'
        ));

        st_astext
    ------------------
     LINESTRING EMPTY

### See Also

ST_IsValid, ST_Collect, ST_CollectionExtract