my @line = (
    [  ## $line[ 0 ]
        [ xxx.xxx, yyy.yyy, zzz.zzz ], ## $line[0][0] (station 0)
        [ xxx.xxx, yyy.yyy, zzz.zzz ], ## (station 1)
        [ xxx.xxx, yyy.yyy, zzz.zzz ],
        ...
    ],
    [   ## Line[ 1 ]
        [ xxx.xxx, yyy.yyy, zzz.zzz ], ## Line[ 1 ][ 0 ]
        [ xxx.xxx, yyy.yyy, zzz.zzz ],
        [ xxx.xxx, yyy.yyy, zzz.zzz ],
        ...
    ],
    ...
);

my( $x, $y, $z ) = $line[ $lineNo ][ $stationNo ];

# Or
use constant{ X => 0, Y => 1, Z => 2 };

my $y = $line[ $lineNo ][ $staionNo ][ Y ];