dms_polygon

syntax

dms_polygon(polygon_data_item)

description

dms_polygon(polygon_data_item) reads each element of the argument under the even-odd rule and writes it back as a valid polygon: clockwise shells, counter-clockwise holes, no vertex on the straight line between its neighbours, and the rings ordered by their first vertex.

It is the clean-up of the dms polygon operators family, and the one that says most plainly what the family is for: the argument does not have to be a valid polygon. Rings may cross themselves, touch themselves, overlap or touch each other, or fail to close, and their orientation is not consulted. A ring shaped like a bow tie comes out as the two triangles it encloses, since the middle is crossed twice; that is the even-odd reading, and it is what the OGC definition the geometry libraries implement leaves undefined.

Geometry that is already valid comes back unchanged apart from vertices that lie on a straight line between their neighbours, which are dropped.

applies to

Attribute polygon_data_item with a polygon Value type: spoint, ipoint, wpoint, upoint, fpoint or dpoint

conditions

The composition type of the argument needs to be polygon.

since version

20.20.0

example

attribute<ipoint> cleaned (district, polygon) := dms_polygon(district/geometry);