Splines interlaced with each other will form many closed areas,the process extracting these closed areas as poly faces is called PiecePoly.
The powerful tools is a great resolution to create seamless joined polygons, operating is also very simple.An UI control is also offered which be used to decide the number of vertices how to change with arc radius.

PieceShapes


Piece_ControlNumVerts

PieceGround

PieceExtend