geos_split_polygon

Geometric functions > geos_split_polygon

syntax

• geos_split_polygon(polygon_data_item)

description

geos_split_polygon(polygon_data_item) splits each multi-polygon element in the polygon_data_item into its individual single-polygon parts. The result is a new domain unit containing one entry per single polygon, with a geometry sub-item holding the polygon geometries and a polygon_rel sub-item that relates each result polygon back to its source element in polygon_data_item.

This operator is useful when polygon data contains multi-part features (multi-polygons) and individual parts are needed as separate entities.

The geos_ prefix of the function name indicates that the implementation of the operator uses geos.

Only dpoint (double precision) coordinates are fully supported for GEOS-based polygon operations. For fpoint coordinates a deprecation warning is issued; use bp_split_polygon instead.

applies to

• attribute polygon_data_item with a polygon value type

conditions

1. The composition type of the polygon_data_item needs to be polygon.
2. The order of points in the polygon_data_item needs to be clockwise for exterior bounds and counterclockwise for holes (right-hand-rule).

result

The result is a container with:

• geometry: polygon attribute with the individual single polygons
• polygon_rel: relation back to the domain of polygon_data_item

since version

14.0

example

unit<uint32> single_parts := geos_split_polygon(district/geometry)
{
    attribute<dpoint>   geometry;
    attribute<district> polygon_rel;
}

see also

• geos_union_polygon
• geos_split_union_polygon
• bp_split_polygon