<?php
/**
 * @author Florian Sternke, www.bananenhand.de/blog/
 * @version 1.0.0.0
 */
class GeoPoint
{
  /**
   * Longitude
   * 
   * @var double
   */
  protected $dblLongitude = 0.0;
  /**
   * Latitude
   * 
   * @var double
   */
  protected $dblLatitude = 0.0;

  /**
   * Initialize an instance of GeoPoint
   *
   * @param double $dblLon Longitude
   * @param double $dblLat Latitude
   */
  public function __construct($dblLon, $dblLat)
  {
    /// You may want to check against a regexp to filter crap like 180.1
    $this->dblLongitude = (double)$dblLon;
    $this->dblLatitude = (double)$dblLat;
  }

  /**
   * Output the point as string (lon,lat)
   *
   * Some strange people (like Google) display coordinates like y,x instead of
   * the logical x,y-way (see cartesian coordinate system). If you prefer the
   * first way, feel free to switch both...
   *
   * @return string
   */
  public function __toString()
  {
    return "({$this->dblLongitude},{$this->dblLatitude})";
  }

  /**
   * Returns the latitude of the geo coord
   *
   * @return double
   */
  public function getLatitude()
  {
    return $this->dblLatitude;
  }

  /**
   * Returns the longitude of the geo coord
   *
   * @return double
   */
  public function getLongitude()
  {
    return $this->dblLongitude;
  }

  /**
   * Transforms the EXIF geo cood array into a decimal format
   * 
   * Array
   * (
   *    [0] => 52/1
   *    [1] => 3367/100
   *    [2] => 0/1
   * )
   * 
   * to 52.561167
   * 
   * @param string $reference N, E, W or S
   * @param array $coordinate Coordinate
   */
  protected static function exifGeoCoordinateToDecimal($reference, array $coordinate)
  {
    list($a,$b) = explode("/", $coordinate[0]);
    list($c,$d) = explode("/", $coordinate[1]);
    list($e,$f) = explode("/", $coordinate[2]);
    $prefix = $reference == 'S' || $reference == 'W' ? -1 : 1;
  
    $a = $b > 0 ? $a / $b : $a;
    $c = $d > 0 ? $c / $d : $c;
    $e = $f > 0 ? $e / $f : $e;
  
    return $prefix * round(($a + ($c * 60 + $e) / 3600), 6); 
  }

  /**
   * Reads an image file and returns the extracted geo information
   * 
   * Reads an image file, transforms the exif geo information into a reusable
   * geo point object
   * 
   * @param string $strFilename File name
   * @return GeoPoint
   * @throws UnexpectedValueException, Exception
   */
  public static function constructFromImageFile($strFilename)
  {
    if (file_exists($strFilename))
    {
      $arrInfos = exif_read_data($strFilename, "EXIF");

      if (is_array($arrInfos["GPSLatitude"]) && is_array($arrInfos["GPSLongitude"]))
      {
        $dblLat = self::exifGeoCoordinateToDecimal($arrInfos["GPSLatitudeRef"], $arrInfos["GPSLatitude"]);
        $dblLon = self::exifGeoCoordinateToDecimal($arrInfos["GPSLongitudeRef"], $arrInfos["GPSLongitude"]);
      
        return new self($dblLon, $dblLat);
      }
      else throw new UnexpectedValueException("Exchangeable image information (EXIF) without GPS data");
    }
    else throw new Exception("File not found");
  }
}

echo GeoPoint::constructFromImageFile("img_0013.jpg");
?>