sub get_bboxes_pdl_bad {
    my $flat      = $sgm-> flat-> setvaltobad( 0 );
    my $idx       = $flat-> qsorti;
    $idx          = $idx-> where( $flat-> index( $idx )-> isgood );
    my ( $runs )  = $flat-> index( $idx )-> rle;
    $runs         = $runs-> where( $runs != 0 )-> cumusumover - 1;
    my ( $x, $y ) = $sgm-> one2nd( $idx );

    my $stop = -1;
    return [ map {
        my $start = $stop + 1;
        $stop     = $_;
        [[ $x( $start:$stop )-> minmax ],
         [ $y( $start:$stop )-> minmax ]]
    } $runs-> list ]
}