#!/usr/bin/perl

use XML::Twig;
use warnings;
use strict;
use utf8;

binmode(STDOUT, ":utf8");

die "Usage: $0 <file.osm>" unless defined $ARGV[0];

my $twig = XML::Twig->new(
    twig_handlers => {
        'node' => \&rotate,
    },
    pretty_print => 'indented',
);

$twig->parsefile($ARGV[0]);
$twig->flush;

sub rotate {
    my ($twig, $elt) = @_;

    my $lon = $elt->att('lon');
    my $lat = $elt->att('lat');

    # do processing
    $lon += 1;
    $lat += 1;

    $elt->set_att('lon', $lon);
    $elt->set_att('lat', $lat);
    $elt->set_att('action', 'modify');

    $elt->flush;
}