#assuming nw,ne,se,sw are convex and clockwise
sub c{
  my($x0,$y0,$x1,$y1,$x2,$y2) = @_;
  $x0 -= $x2;
  $x1 -= $x2;
  $y0 -= $y2;
  $y1 -= $y2;
  return $x1*$y0 > $x0*$y1;
}


unless( c(@nw,@ne,@find)
     && c(@ne,@se,@find)
     && c(@se,@sw,@find)
     && c(@sw,@nw,@find)
){
   die "data is outside of the quadrant\n";
}
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