STV_ForceLHR

Alters the order of the vertices of a spatial object to follow the left-hand-rule.

Alters the order of the vertices of a spatial object to follow the left-hand-rule.

Behavior type

Immutable

Syntax

STV_ForceLHR( g, [USING PARAMETERS skip_nonreorientable_polygons={true | false} ])

Arguments

g
Spatial object, type GEOGRAPHY.
skip_nonreorientable_polygons = { true | false }

(Optional) Boolean

When set to False, non-orientable polygons generate an error. For example, if you use STV_ForceLHR or STV_Reverse with skip_nonorientable_polygons set to False, a geography polygon containing a hole generates an error. When set to True, the result returned is the polygon, as passed to the API, without alteration.

This argument can help you when you are creating an index from a table containing polygons that cannot be re-oriented.

Vertica Place considers these polygons non-orientable:

  • Polygons with a hole

  • Multipolygons

  • Multipolygons with a hole

Default value: False

Returns

GEOGRAPHY

Supported data types

Data Type GEOMETRY GEOGRAPHY (Perfect Sphere) GEOGRAPHY (WGS84)
Point No No No
Multipoint No No No
Linestring No No No
Multilinestring No No No
Polygon No Yes Yes
Multipolygon No Yes Yes
GeometryCollection No No No

Examples

The following example shows how you can use STV_ForceLHR.

Re-orient a geography polygon to left-hand orientation:

=> SELECT ST_AsText(STV_ForceLHR(ST_GeographyFromText('Polygon((1 1, 3 1, 2 2, 1 1))')));
            ST_AsText
--------------------------------
 POLYGON ((1 1, 3 1, 2 2, 1 1))
(1 row)

Reverse the orientation of a geography polygon by forcing left-hand orientation:

=> SELECT ST_AsText(STV_ForceLHR(ST_GeographyFromText('Polygon((1 1, 2 2, 3 1, 1 1))')));
           ST_AsText
--------------------------------
 POLYGON ((1 1, 3 1, 2 2, 1 1))
(1 row)

See also

STV_Reverse