Sector2D is the class for all objects that store a 2D sector defined by a
outer bounding rectangle, width, start angle, and angular extent (length of
the arc).
Sector2D() -
Constructor for class ca.utoronto.cs.prefuseextensions.geom.Sector2D
TreeLayout instance that computes a radial space filling layout,
laying out subsequent depth levels of a tree on circles of progressively increasing radius.