How to save GPS coordinates in exif data on Android?

Question

I am writing GPS coordinates to my JPEG image, and the coordinates are correct (as demonstrated by my logcat output) but it appears that it's being corrupted somehow. Reading the exif data results in either null values or, in the case of my GPS: 512.976698 degrees, 512.976698 degrees. Can anyone shed some light on this problem?

writing it:

        try {             ExifInterface exif = new ExifInterface(filename);             exif.setAttribute(ExifInterface.TAG_GPS_LATITUDE, latitude);             exif.setAttribute(ExifInterface.TAG_GPS_LONGITUDE, longitude);             exif.saveAttributes();             Log.e("LATITUDE: ", latitude);             Log.e("LONGITUDE: ", longitude);           } catch (IOException e) {             e.printStackTrace();         } 

and reading it:

        try {             ExifInterface exif = new ExifInterface("/sdcard/globetrotter/mytags/"+ TAGS[position]);             Log.e("LATITUDE EXTRACTED", exif.getAttribute(ExifInterface.TAG_GPS_LATITUDE));             Log.e("LONGITUDE EXTRACTED", exif.getAttribute(ExifInterface.TAG_GPS_LONGITUDE));         } catch (IOException e) {             e.printStackTrace();         } 

It goes in (for example) 37.715183, -117.260489 and comes out 33619970/65540, 14811136/3368550, 33619970/65540, 14811136/3368550. Am I doing it wrong?

EDIT:

So, the problem is I am not encoding it in the properly defined format, which is something like you see here:

Can anyone explain what this format is? Obviously the first number is 22/1 = 22 degrees, but I can't figure out how to compute the decimal there.

Answer 1

GPSLatitude

Indicates the latitude. The latitude is expressed as three RATIONAL values giving the degrees, minutes, and seconds, respectively. If latitude is expressed as degrees, minutes and seconds, a typical format would be dd/1,mm/1,ss/1. When degrees and minutes are used and, for example, fractions of minutes are given up to two decimal places, the format would be dd/1,mmmm/100,0/1.

https://docs.google.com/viewer?url=http%3A%2F%2Fwww.exif.org%2FExif2-2.PDF

The Android docs specify this without explanation: http://developer.android.com/reference/android/media/ExifInterface.html#TAG_GPS_LATITUDE

Exif data is standardized, and GPS data must be encoded using geographical coordinates (minutes, seconds, etc) described above instead of a fraction. Unless it's encoded in that format in the exif tag, it won't stick.

How to encode: http://en.wikipedia.org/wiki/Geographic_coordinate_conversion

How to decode: http://android-er.blogspot.com/2010/01/convert-exif-gps-info-to-degree-format.html

Answer 2

Here is some code I've done to geotag my pictures. It's not heavily tested yet, but it seems to be ok (JOSM editor and exiftool read location).

ExifInterface exif = new ExifInterface(filePath.getAbsolutePath()); exif.setAttribute(ExifInterface.TAG_GPS_LATITUDE, GPS.convert(latitude)); exif.setAttribute(ExifInterface.TAG_GPS_LATITUDE_REF, GPS.latitudeRef(latitude)); exif.setAttribute(ExifInterface.TAG_GPS_LONGITUDE, GPS.convert(longitude)); exif.setAttribute(ExifInterface.TAG_GPS_LONGITUDE_REF, GPS.longitudeRef(longitude)); exif.saveAttributes(); 

And class GPS is here. (method could be shorter, but it's readable at least)

/*  * @author fabien  */ public class GPS {     private static StringBuilder sb = new StringBuilder(20);      /**      * returns ref for latitude which is S or N.      * @param latitude      * @return S or N      */     public static String latitudeRef(double latitude) {         return latitude<0.0d?"S":"N";     }      /**      * returns ref for latitude which is S or N.      * @param latitude      * @return S or N      */     public static String longitudeRef(double longitude) {         return longitude<0.0d?"W":"E";     }      /**      * convert latitude into DMS (degree minute second) format. For instance<br/>      * -79.948862 becomes<br/>      *  79/1,56/1,55903/1000<br/>      * It works for latitude and longitude<br/>      * @param latitude could be longitude.      * @return      */     synchronized public static final String convert(double latitude) {         latitude=Math.abs(latitude);         int degree = (int) latitude;         latitude *= 60;         latitude -= (degree * 60.0d);         int minute = (int) latitude;         latitude *= 60;         latitude -= (minute * 60.0d);         int second = (int) (latitude*1000.0d);          sb.setLength(0);         sb.append(degree);         sb.append("/1,");         sb.append(minute);         sb.append("/1,");         sb.append(second);         sb.append("/1000");         return sb.toString();     } }