Categories:

Geospatial functions

ST_ISVALID

Returns TRUE if the specified GEOGRAPHY or GEOMETRY object represents a valid shape. Examples of invalid shapes include shapes with self-intersections and spikes.

Syntax

ST_ISVALID( <geography_or_geometry_expression> )
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Arguments

geography_or_geometry_expression

The argument must be an expression of type GEOGRAPHY or GEOMETRY.

Returns

Returns a BOOLEAN value.

Usage notes

  • ST_ISVALID only checks for the validity of a shape. It doesn’t modify data. When constructing objects from spatial formats (such as WKT, WKB, EWKT, EWKB, or GeoJSON), conversion functions (for example, TO_GEOGRAPHY, TO_GEOMETRY, ST_GEOGRAPHYFROMWKT, or ST_GEOMETRYFROMWKT) parse input and by default attempt to validate or repair shapes. If a conversion function can’t repair a shape, it returns an error unless you accept invalid shapes.

  • To ingest data that might be invalid (for example, data that you plan to correct later), specify TRUE for the additional allow_invalid argument when you call the conversion function to allow an invalid shape. You can then use the ST_ISVALID function to flag invalid rows in a table.

  • Some geospatial functions might return an error or unusable results when given invalid shapes. Use the ST_ISVALID function to check validity. You can correct invalid shapes before performing spatial analytics.

  • When shapes are invalid, simple corrections include buffering with a small positive or negative distance (for example, to remove tiny spikes or resolve self-intersections) and then rechecking validity using the ST_ISVALID function.

Examples

The following examples use the ST_ISVALID function.

Determine whether a polygon is a valid shape:

SELECT ST_ISVALID( TO_GEOGRAPHY('POLYGON((-93.086 37.557,-86.699 37.497,-93.198 35.123,-93.086 37.557))') ) AS is_valid;
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+----------+ | IS_VALID | |----------| | True | +----------+ 
SELECT ST_ISVALID( TO_GEOGRAPHY( 'POLYGON((-92.799 37.601,-88.240 37.617,-92.733 36.198,-88.305 36.171,-92.799 37.601))', TRUE) ) AS is_valid;
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+----------+ | IS_VALID | |----------| | False | +----------+

Correct an invalid shape by using the ST_BUFFER function to add small buffer:

WITH g AS ( SELECT TO_GEOMETRY('POLYGON((0 0, 2 2, 2 0, 0 2, 0 0))', TRUE) AS geom ) SELECT ST_ISVALID(geom) AS is_valid_before_buffer, ST_ISVALID(ST_BUFFER(geom, -0.001)) AS is_valid_after_buffer FROM g;
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+------------------------+-----------------------+ | IS_VALID_BEFORE_BUFFER | IS_VALID_AFTER_BUFFER | |------------------------+-----------------------| | False | True | +------------------------+-----------------------+
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