sub is_clockwise
{
  # $verts and $edges are arrayrefs
  my ($verts, $edges) = @_;

  my @sorted  = sort {$a->{y} > $b->{y}} @$verts;
  my $highest = $sorted->[0];

  my ($edge_1, $edge_2) = &get_adjacent($edges, $highest);

  if(&right_turn($edge_1, $edge_2)) {
    return true; # clockwise!
  } else {
    return false; # counterclockwise?
  }
}