Geometry

Convex Hull	Converts the selected items into convex Polygon, LineString or Point items.
Alpha Shape	Converts the selected items into Alpha shapes (concave hulls), using Edelsbrunner's algorithm.
Chi Shape	Converts the selected items into Chi shapes (concave hulls), using Duckham's algorithm.
'Dig' Shape	Converts the selected items into 'dig' shapes (concave hulls), using Park/Oh's algorithm.
Straight Skeleton	Creates the 'straight skeleton' of a Polygon or MultiPolygon.
Medial Axis	Creates the 'medial axis' of a Polygon or MultiPolygon.