my ($x,$y,$redline);
while (<FILE>) {
   if ($redline) {
      ($x,$y) = /at location (\S+) (\S+)/;
      print "$x $y\n";
   }
   $redline = /red line/;
}
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Vary the details as needed. $redline is set to a true value when ever the pattern matches (and a false value when it doesn't match) so that on the next iteration of the loop, you'll be able to capture the location information.