A close loop with optional rings

rings t returns the linear rings contained in t (a Polygon object)

exterior_ring t returns the first linear ring contained in t (a Polygon object). This ring bounds the surface

If t (a Polygon object) contains more than 1 linear ring, interior_rings t returns the rest of the linear rings apart from the first. These rings (if present), bound the holes.

Create a polygon object from an array of close line strings (note no checking is down here to ensure the loops are indeed closed.)

Convert directly to the positions that make up the lines.

Convert directly from positions to lines