ST_ToPolygon method

geometry-expression.ST_ToPolygon()

ST_Polygon If the geometry-expression is of type ST_Polygon, returns the geometry-expression. If the geometry-expression is of type ST_CurvePolygon, returns geometry-expression.ST_CurvePolyToPoly(). If the geometry-expression is a geometry collection with a single element of type ST_CurvePolygon, returns that element. If the geometry-expression is the empty set, returns an empty set of type ST_Polygon. Otherwise, raises an exception condition.
The spatial reference system identifier of the result is the same as the spatial reference system of the geometry-expression.

Convert the geometry to a polygon. The logic is equivalent to that used for CAST( geometry-expression AS ST_Polygon ). If the geometry-expression is a curve polygon, it is interpolated using ST_CurvePolyToPoly().

If geometry-expression is already known to be an ST_Polygon value, it is more efficient to use TREAT( geometry-expression AS ST_Polygon ) than the ST_ToPolygon method.

Note

By default, ST_ToPolygon uses the original format for a geometry, if it is available. Otherwise, the internal format is used. For more information about internal and original formats, see STORAGE FORMAT clause, CREATE SPATIAL REFERENCE SYSTEM statement.

SQL/MM (ISO/IEC 13249-3: 2006) 5.1.33

The following example returns the result Polygon EMPTY.

SELECT NEW ST_GeomCollection().ST_ToPolygon()

The following returns an error because the Shape column is of type ST_Geometry and ST_Geometry does not support the ST_Area method.

SELECT Shape.ST_Area()
FROM SpatialShapes WHERE ShapeID = 22

The following uses ST_ToPolygon to change the type of the Shape column expression to ST_Polygon. ST_Area returns the result 12.5.

SELECT Shape.ST_ToPolygon().ST_Area()
FROM SpatialShapes WHERE ShapeID = 22

In this case, the value of the Shape column is known be of type ST_Polygon, so TREAT can be used to efficiently change the type of the expression. ST_Area returns the result 12.5.

SELECT TREAT( Shape AS ST_Polygon ).ST_Area() 
FROM SpatialShapes WHERE ShapeID = 22

ST_ToPolygon method

Syntax

Returns

Remarks

Note

See also

Standards and compatibility

Example