How to parse KML files using perl?

Question

I am trying to parse a KML file using perl. I am trying to use XML::Simple module for doing this.

I want to go through each placemarker and extract some data namely

1) Mcode
2) coordinates

After reading several posts, I tried the following just to print the coordinates of all the points, but it fails

use strict;
use warnings;
use XML::Simple;
use Data::Dumper;

my $myFile = XMLin('ExperimentMap.kml');

foreach my $folder (@{$myFile->{Document}->{Folder}->{Placemark}})  {
    print $folder->{Point}->{coordinates}."\n";
}

I am using the following KML:

<?xml version='1.0' encoding='UTF-8'?>
<kml xmlns='http://www.opengis.net/kml/2.2'>
    <Document>
        <name>ExperimentMap</name>
        <description><![CDATA[]]></description>
        <Folder>
            <name>ExperimentLayer</name>
            <Placemark>
                <styleUrl>#icon-503-FF8277</styleUrl>
                <name>home</name>
                <ExtendedData>
                    <Data name='string'>
                        <displayName>Mcode</displayName>
                        <value>PLAAB</value>
                    </Data>
                </ExtendedData>
                <ExtendedData>
                    <Data name='string'>
                        <displayName>postal code</displayName>
                        <value>450010</value>
                    </Data>
                </ExtendedData>
                <description><![CDATA[my home


Mcode: PLAAB
postal code: 450010]]></description>
                <Point>
                    <coordinates>80.23435592651367,13.094024942328286,0.0</coordinates>
                </Point>
            </Placemark>
            <Placemark>
                <styleUrl>#icon-503-FF8277</styleUrl>
                <name>shop</name>
                <ExtendedData>
                    <Data name='string'>
                        <displayName>Mcode</displayName>
                        <value>XMPLE</value>
                    </Data>
                </ExtendedData>
                <ExtendedData>
                    <Data name='string'>
                        <displayName>postal code</displayName>
                        <value>450013</value>
                    </Data>
                </ExtendedData>
                <description><![CDATA[my shop


Mcode: XMPLE
postal code: 450013]]></description>
                <Point>
                    <coordinates>80.2437973022461,13.106230102044576,0.0</coordinates>
                </Point>
            </Placemark>
            <Placemark>
                <styleUrl>#icon-503-FF8277</styleUrl>
                <name>place3</name>
                <ExtendedData>
                    <Data name='string'>
                        <displayName>Mcode</displayName>
                        <value>UDKBL</value>
                    </Data>
                </ExtendedData>
                <ExtendedData>
                    <Data name='string'>
                        <displayName>postal code</displayName>
                        <value>578635</value>
                    </Data>
                </ExtendedData>
                <description><![CDATA[my school


Mcode: UDKBL
postal code: 578635]]></description>
                <Point>
                    <coordinates>80.24688720703125,13.096198508196448,0.0</coordinates>
                </Point>
            </Placemark>
        </Folder>
        <Style id='icon-503-FF8277'>
            <IconStyle>
                <color>ff7782FF</color>
                <scale>1.1</scale>
                <Icon>
                    <href>http://www.gstatic.com/mapspro/images/stock/503-wht-blank_maps.png</href>
                </Icon>
            </IconStyle>
        </Style>
    </Document>
</kml>

Answer 1

How about:

while (my ($key, $folder) = each %{$myFile->{Document}{Folder}{Placemark}})  {
    print $folder->{Point}->{coordinates}."\n";
}

output:

80.2437973022461,13.106230102044576,0.0
80.24688720703125,13.096198508196448,0.0
80.23435592651367,13.094024942328286,0.0

In your code, you're using

foreach my $folder (@{$myFile->{Document}->{Folder}->{Placemark}})  {
    print $folder->{Point}->{coordinates}."\n";
}

assuming $myFile->{Document}->{Folder}->{Placemark} is a reference to an array. But it isn't, it is a reference to a hash, so you have to walk thru it and foreach pair of (key,value) extract the coordinate from the value.

Answer 2

I don't think I would use XML::Simple for this.

With XML::Twig this is what you would write:

#!/usr/bin/perl

use strict;
use warnings;

use 5.10.0; # to get 'say'

use XML::Twig;

XML::Twig->new( twig_roots => { coordinates => sub { say $_->text; } })
         ->parsefile( $ARGV[0]);

Answer 3

Another possibility is to use XML::LibXML and XPaths. The advantage of XPaths is that these are also available to other languages, so other developer may understand your code. The disadvantage of XPaths is that their usage is not anymore nice in presence of namespaces (which is the case here), leading to some ugly-looking workarounds like using the local-name() function.

Here's a sample script:

use XML::LibXML;
my $doc = XML::LibXML->new->parse_file('ExperimentMap.kml');
for my $coordinate_node ($doc->findnodes('//*[local-name()="coordinates"]')) {
    print $coordinate_node->textContent, "\n";
}