Google Geocoding

This is a little experiment with the Google Geocoding service. Geocoding is the process of turning human readable addresses into a latitude and longitude. Google provide a free web service to let you do this very easily.

As a supporting utlity for the Google Maps service, Google Geocoding is a very handy mechanism for easily obtaining the latitude and longitude of pretty much any point on the planet.

To do the geocoding calls I have a simple class that has a couple of methods like this:

public function query($location)
{
    $url    = $this->_queryUrl($location);
    $xml = simplexml_load_file($url);
    if (false == ($xml instanceof SimpleXMLElement))
    {
        throw new Google_Exception('Geocoding api call failed');
    }
    $response   = new Geocoding_Response($url, $xml);
    return $response;
}
protected function _queryUrl($location)
{
    $key  = $this->getApiKey();
    $url  = 'http://' . self::$_BaseUrl . '/maps/geo?output=xml&oe=utf-8&key' . $key . '&q=' . $location;
    return $url;
}

I also have a little response class to wrap and parse the XML data. Its very basic but you could make it do all sorts of things.

class Geocoding_Response
{
    protected $_url;
    protected $_xml;
    protected $_error;
    protected $_responseError;
    protected $_coords;
    public function __construct($url, SimpleXMLElement $xml)
    {
        $this->_url     = $url;
        $this->_coords  = array();
        $this->_processXml($xml);
    }
    public function hasError()
    {
        return $this->_error;
    }
    public function responseError()
    {
        return $this->_responseError;
    }
    public function lat()
    {
        return $this->_coords['lat'];
    }
    public function lng()
    {
        return $this->_coords['lng'];
    }
    public function url()
    {
        return $this->_url;
    }
    public function __toString()
    {
        return implode(', ', $this->_coords);
    }
    protected function _processXml(SimpleXMLElement $xml)
    {
        $this->_xml = $xml;
        if (200 != (int) $xml->Response->Status->code)
        {
            $this->_error = true;
            $this->_responseError = $this->_statusMessage((int) $xml->Response->Status);
        }
        list($lng, $lat) = explode(',', (string) $this->_xml->Response->Placemark->Point->coordinates);
        $this->_coords  = array('lat' => $lat, 'lng' => $lng);
        return true;
    }
    protected function _statusMessage($status)
    {
        switch ($status)
        {
            case 200:
                return 'ok';
            case 400:
                return 'bad request';
            case 500:
                return 'internal error';
            case 601:
                return 'no location provided';
            case 602:
                return 'location not found';
            case 603:
                return 'location unavailable';
            case 604:
                return 'unknown directions';
            case 610:
                return 'bad api key';
            case 620:
                return 'too many queries';
            default:
                return 'Unknown error';
        }
    }
}

To do some geocoding you first get a Google Maps API key (slightly odd since we're doing this server side but still...). Then you would use the above code like this:

$location = '10 Downing Street, London';
$geo = new Google_Geocoding($apiKey);
try {
    $response = $geo->query($location);
    echo $response;
}
catch (Google_Exception $ex) {
    echo "Error";
}

There's a demo of this code working here.