Question

Is there any fairly fast php code to convert a city + country to latitude and longitude coordinates. I have a list of locations and I need to convert them to coordinates. I tried doing it in javascript, but I encountered some problems trying to get the results back to php to store it in my JSON file. So is there any efficient PHP code to do this?

Thanks.

Answer 1

In my app, I’m using the following function to geo-code locations using google service. The function takes one parameter – location to geo-code (e.g. “Boston, USA” or “SW1 1AA, United Kingdom”) and returns an associative array with Lat/Lon. If an error occurs or location cannot be determined, then it returns FALSE.

Note that in many cases city + country will not be able to determine the location uniquely. For example, there are probably 100 cities named Springfield in the USA alone. Also, when passing country to a geo-coding service, make sure to put the full country name and not a 2-letter code. I found this the hard way: I was passing ‘CA’ for “Canada” and was getting strange results. Apparently, google assumed that ‘CA’ means “California”.

function getGeoLocationGoogle($location)
{
    $url = "http://maps.googleapis.com/maps/api/geocode/xml?address=". urlencode($location) . "&sensor=false";
    $userAgent = "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 FirePHP/0.4";

    //Setup curl object and execute
    $curl = curl_init($url);
    curl_setopt($curl, CURLOPT_USERAGENT, $userAgent);
    curl_setopt($curl, CURLOPT_FAILONERROR, true);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    $result = curl_exec($curl);

    $req = $location;

    //Process response from Google servers
    if (($error = curl_errno($curl)) > 0)
    {
        return FALSE;
    } 

    $geo_location = array();
    //Try to convert XML response into an object
    try
    {
        $xmlDoc = new DOMDocument();
        $xmlDoc->loadXML($result);
        $root = $xmlDoc->documentElement;

        //get errors
        $status = $root->getElementsByTagName("status")->item(0)->nodeValue;
        if($status != "OK")
        {
            $error_msg = "Could not determine geographical location of $location - response code $status";
        }
        $location = $root->getElementsByTagName("geometry")->item(0)->getElementsByTagName("location")->item(0);
        if(!$location)
        {
            return FALSE;
        }

        $xmlLatitude = $location->getElementsByTagName("lat")->item(0);
        $valueLatitude = $xmlLatitude->nodeValue;
        $geo_location['Latitude'] = $valueLatitude; 

        //get longitude
        $xmlLongitude = $location->getElementsByTagName("lng")->item(0);
        $valueLongitude = $xmlLongitude->nodeValue;
        $geo_location['Longitude'] = $valueLongitude;

        //return location as well - for good measure
        $geo_location['Location'] = $req;
    }
    catch (Exception $e)
    {
        return FALSE;
    }       

    return $geo_location;
}