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Created Jun 10, 2012
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Filter out OpenAir airspace above specified flight level
#!/bin/perl -w
use strict;
sub emit($$) {
my ($ceiling, $stanza) = @_;
if ($stanza =~ /^AL (.*)/im and $1 =~ /^FL\s*(\d+)$/i) {
return if $1 >= $ceiling;
print $stanza;
if (@ARGV == 0 or $ARGV[0] !~ /^(?:FL)?(\d+)$/) {
print STDERR <<EOF;
Usage: $0 CEILING [FILE]...
Filter OpenAir data to remove blank lines, comments, and stanzas whose floor
is at or above the flight level CEILING. For example, using a value of 75 (or
FL75) for CEILING will remove all data for airspace which does not extend
below flight level 75. Stanzas whose floor is not expressed as a flight level
are not filtered, but will be below the transition altitude in any case.
exit 64;
my ($ceiling, $stanza) = ($1, "");
while (my $line = <>) {
chomp $line;
$line =~ s/\s*(\*.*)?$//;
$line =~ s/\s+/ /g;
if ($line =~ /^AC /) {
emit $ceiling, "$stanza\n" if length $stanza;
$stanza = "";
$stanza .= "$line\n" if length $line;
emit $ceiling, $stanza if length $stanza;
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