Offset distance:

NOTE: for purposes of offset, Polygons are always "oriented"- counterclockwise rings are reversed to produce uniformly clockwise rings. This means a negative offset will expand Polygons whereas a positive offset will contract them.

Join type: miter miter limit (in units of offset distance) bevel round square
Join type demo angle: Measured as the angle between
the tangent vectors of the segments
before and after the vertex