ST_Perimeter method for type ST

ST_Perimeter method for type ST_MultiSurface

Computes the perimeter of the multi-surface in the specified units.

Syntax

multisurface-expression.ST_Perimeter([ unit-name])

Parameters

Name	Type	Description
unit-name	VARCHAR(128)	The units in which the perimeter should be computed. Defaults to the unit of the spatial reference system. The unit name must match the UNIT_NAME column of a row in the ST_UNITS_OF_MEASURE view where UNIT_TYPE is 'LINEAR'.

Remarks

The ST_Perimeter method returns the length of the perimeter of a multi-surface in the units identified by the unit-name parameter. If the multi-surface is empty, then NULL is returned.

If the multi-surface contains Z values, these are not considered when computing the perimeter of the geometry.

The perimeter of a polygon includes the length of all rings (exterior and interior).

Note

If the multisurface-expression is an empty geometry (ST_IsEmpty()=1), then this method returns NULL.

Note

By default, ST_Perimeter 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.

Standards and compatibility

Example

The following example creates a multi-surface containing two polygons and uses ST_Perimeter to find the length of the perimeter, returning the result 44.

SELECT NEW ST_MultiSurface( NEW ST_Polygon('Polygon((0 0, 1 0, 1 1,0 1, 0 0))')
			  , NEW ST_Polygon('Polygon((10 10, 20 10, 20 20,10 20, 10 10))') )
		.ST_Perimeter()

The following example creates a multi-surface containing two polygons and an example unit of measure (example_unit_halfmetre). The ST_Perimeter finds the length of the perimeter, returning the value 88.0.

CREATE SPATIAL UNIT OF MEASURE IF NOT EXISTS  "example_unit_halfmetre" TYPE LINEAR CONVERT USING .5;
SELECT NEW ST_MultiSurface( NEW ST_Polygon('Polygon((0 0, 1 0, 1 1,0 1, 0 0))')
			  , NEW ST_Polygon('Polygon((10 10, 20 10, 20 20,10 20, 10 10))') )
		.ST_Perimeter('example_unit_halfmetre');

Discuss this page in DocCommentXchange.