my @bandWidth= ( 3, 15, 0 );

sub BuildKey {
    my( $radius, $x, $y, $z )= @_;
    my $sizeRange=
        $radius <= 2 ? 0
      : $radius <= 10 ? 1
      : 2;
    my $width= $bandWidth[$sizeRange];
    if(  0 == $width  ) {
        return ConcatForKey( $sizeRange, 0, 0, 0 );
    }
    return ConcatForKey(
        $sizeRange, int($x/$width), int($y/$width), $z );
}