Point order in polygons

For some functions (like union_polygon) the sequence order of points in a polygon matters.

rules

The following rules apply to the sequence of points in a polygon:

1. outer rings need to be configured clock wise
2. inner rings (lakes) are configured counter clock wise
3. the first and the last point need to have the same coordinate

If the sequence of points is configured manually and used in the sequence2points, always configure the correct sequence, although for the map and functions like point_in_polygon an incorrect sequence might not matter.

validation

A way to test if the correct sequence is configured is by requesting the area of the polygon with the area function. A positive value indicates a correct sequence, a negative value indicates the points are configured in the incorrect sequence