sub rotate {
    my ( $x,$y,$z,$angle ) = @_;
    $angle = deg2rad($angle);
    my $x_new = cos($angle)*$x - sin($angle)*$y;
    my $y_new = sin($angle)*$x + cos($angle)*$y;
  return $x_new, $y_new, $z;
}
sub deg2rad { return 3.14159265358979*$_[0]/180 };