Vertex(final Vector2D location){
  this.location=location;
  this.incoming=null;
  this.outgoing=null;
  this.lines=new ArrayList<Line>();
}

Vertex ( final Vector2D location ) { this . location = location ; this . incoming = null ; this . outgoing = null ; this . lines = new ArrayList < Line > ( ) ; }
build a non - processed vertex not owned by any node yet .
