Split GPX file

GPX-files are used to store planned and done routes, for example for cycling.
A lot of web sites and applications allow creating and editing such routes.

In practice it matters for a trip from A to B if there is one long route that covers the whole distance or many shorter routes. Long routes get hard to handle, because of the software gets slow or crashes when the data set is too big. And small routes are more difficult to use when wanting to have an overview and they require switching to another route during the day, which can be inconvenient.

In theory it is possible to just copy a long route and to delete parts of it to obtain shorter routes, but that does not work too well, if the route is already very long.

So one way to go is to make a long route with only rough planning, to have an overview and then split it into shorter routes that can then be modified to obtain a more accurate planning.
So the following program (written in Perl for Linux) will split a GPX file into n about equally long parts. It is quite simple, but I hope it will help to make this task a little bit easier.

License is GPL v3.

GITHUB

#!/usr/bin/perl -w

# (C) Karl Brodowsky 2024-06-09
# Licence GPS v3.0
# (see https://www.gnu.org/licenses/gpl-3.0.de.html )

use strict;
use utf8;
use Encode qw(decode encode);

binmode STDOUT, ":utf8";
binmode STDIN, ":utf8";

my $header =<<'EOH';
<?xml version='1.0' encoding='UTF-8'?>
<gpx version="1.1" creator="https://www.komoot.de" xmlns="http://www.topografix.com/GPX/1/1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd">
  <metadata>
    <name><<TITLE>></name>
    <author>
      <link href="https://www.komoot.de">
        <text>komoot</text>
        <type>text/html</type>
      </link>
    </author>
  </metadata>
  <trk>
    <name><<TITLE>></name>
    <trkseg>
EOH
my $footer =<<'EOF';
    </trkseg>
  </trk>
</gpx>
EOF

sub usage($) {
    my $msg = $_[0];
    if ($msg) {
        chomp $msg;
        print $msg, "\n\n";
    }
    print <<"EOU";
USAGE

$0 <<FILE>> <<NAME>> <<NUMBER_OF_PARTS>>
EOU

    if ($msg) {
        exit 1;
    } else {
        exit 0;
    }
}

if (scalar(@ARGV) == 0 || $ARGV[0] =~ m/^-{0,2}help/) {
    usage("");
}
if (scalar(@ARGV) != 3) {
    usage("wrong number of arguments");
}
my $file = $ARGV[0];
my $file_u = decode("utf-8", $file);
unless (-f $file && -r $file) {
    usage("$file_u is not a readable file");
}
unless ($file =~ m/.+\.gpx$/) {
    usage("$file_u is not a gpx-file");
}
my $name = decode("utf-8", $ARGV[1]);
$name =~ s/^\s+//;
$name =~ s/\s+$//;
$name =~ s/\r//g;

unless (length($name) > 0) {
    usage("$name must be at least 1 character");
}
if ($name =~ m/[<>"']/) {
    usage("$name contains illegal characters");
}
print "name=$name\n";

my $number_of_parts = $ARGV[2];
if ($number_of_parts < 2) {
    usage("at least 2 parts are required");
}

open INPUT, "<:utf8", $file || usage("cannot open $file_u");
my @points = ();
my $point = "";
while (<INPUT>) {
    if (m/^\s*<trkpt/) {
        $point = $_;
    } elsif (m/^\s*<(ele|time)>/) {
        $point .= $_;
    } elsif (m/^\s*<\/trkpt>/) {
        $point .= $_;
        push @points, $point;
        $point = "";
    } else {
        print;
    }
}
close INPUT;
print "\n";

my $length = scalar(@points);

sub part_length($$) {
    my ($remaining_length, $remaining_number_of_parts) = @_;
    ($remaining_length - 1) / $remaining_number_of_parts + 1;
}

my $part_length = part_length($length, $number_of_parts);
print "length = $length part_length = $part_length number_of_parts = $number_of_parts\n";

if ($part_length < 2) {
    usage("too many parts part_length=$part_length");
}
my $remaining_length;
my $remaining_number_of_parts = $number_of_parts;
my $i = 0;
while ($remaining_number_of_parts > 0) {
    $remaining_length=scalar(@points);
    $part_length = int(part_length($remaining_length, $remaining_number_of_parts) + 0.5);
    my $header_i = $header;
    my $title_i = sprintf("%s (%d)", $name, $i);
    $header_i =~ s/<<TITLE>>/$title_i/g;
    my $file_i = $file;
    my $file_u_i = decode("utf-8", $file);
    $file_i =~ s/\.gpx$/_$i.gpx/;
    print "i=$i remaining_number_of_parts=$remaining_number_of_parts remaining_length=$remaining_length\n";
    print "i=$i file_i=$file_u_i title_i=$title_i\n";
    open OUTPUT, ">:utf8", $file_i;
    print OUTPUT $header_i;
    for (my $j = 0; $j < $part_length; $j++) {
        my $point = $points[0];
        if ($j < $part_length -1) {
            shift @points;
        }
        print OUTPUT $point;
    }
    print OUTPUT $footer;
    close OUTPUT;
    $i++;
    $remaining_number_of_parts--;
}

P.S. I plan to return to regular posts in this blog during this year.