Phoca Forum

Code: Select all

Extracting the coordinates from the image file
Picasa stores the coordinates inside a special area inside the image file called Exif, designed to store meta information about the images. It is usually used to store the camera model, the settings of the camera and the date when the picture was taken. Exif is a common standard and also allows us to include geotagging information. Extracting this information with PHP is quite easy because PHP provides us with an easy to use module for reading Exif data.

$exif = exif_read_data($filename, 'EXIF');

var_dump($exif['GPSLatitude']);
-> array(3) { [0]=> string(4) "41/1" [1]=> string(4) "53/1" [2]=> string(8) "25/1" }

var_dump($exif['GPSLatitudeRef']);
-> string(1) "N"

var_dump($exif['GPSLongitude']);
-> array(3) { [0]=> string(4) "12/1" [1]=> string(4) "29/1" [2]=> string(8) "32/1" }

var_dump($exif['GPSLongitudeRef']);
-> string(1) "E"

After obtaining the raw coordinates from the Exif data we need to convert it to something that we can use. I use two helper functions - one to convert the degrees, minutes and seconds to fractional decimal numbers - Exif stores numbers as actual fractions - and one to convert these three to a single fractional decimal degree. This is the format that we can use for all kinds of fun stuff. All of this is wrapped into a single function called getCoordinates(). The result of this function is an array containing the latitude and longitude of the specified file.

if ($c = getCoordinates($filename)) {
$latitude = $c[0];
$longitude = $c[1];