PHP - Extract XML data to a 2d array

I was wondering if someone could give me a hand.

I have a KML file ( Google Maps XML ) ... I need to extract the coordinates to a 2D array.

The format of the file is as follows:

<?xml version="1.0" encoding="UTF-8"?>
<kml
    xmlns="http://ift.tt/1b6BtQH">
    <Document>
        <Placemark>
            <name>Im a name</name>
            <Point>
                <coordinates>138.611798,-34.926053</coordinates>
            </Point>
        </Placemark>
        <Placemark>
            <name>Im a name</name>
            <Point>
                <coordinates>138.611798,-34.926053</coordinates>
            </Point>
        </Placemark>
        <Placemark>
            <name>Im a name</name>
            <Point>
                <coordinates>138.611798,-34.926053</coordinates>
            </Point>
        </Placemark>
        [...]

I need to be able to return an array with the following format

Array
(
    [0] => Array
        (
            [0] => 138.611798
            [1] => -34.926053
        )
    [1] => Array
        (
            [0] => 138.611798
            [1] => -34.926053
        )

My kml file will contain quite a few points so i need to be able to do this automatically.

Any help would be really appreciated.

Thanks