October 16th 2014, Exiv2

October 15th 2014 Android Storage | | October 18th 2014 GPS Altitude Correction

Currently, the base Qt package does not support EXIF tags. The “Qt Extended” project used to provide a QExifImageHeader class, but the actual status is that it has been discontinued by Qt in 2009. Although it is still developed as a fork under “Qt Extended Improved” I doubt that it will be 100% compatible with the upcoming Qt 5.4 release, so I am shying away from backporting it.

Instead let’s have a look at the Exiv2 library: It is a GPLed C++ library with CMake support, which adds support for EXIF tags in all major image formats.


To compile, first let’s install the development packages libjpeg-dev, libpng-dev, libtiff-dev and libexpat1-dev. Then we check out Exiv2 via subversion and compile it CMake-style:

sudo apt-get install libjpeg-dev libpng-dev libtiff-dev libexpat1-dev

svn checkout svn://dev.exiv2.org/svn/trunk libexiv2
cd libexiv2

cmake .
sudo make install

Usage Example

We simply would like to add a GPSAltitude tag to a JPEG file. According to the tag reference documentation, the tag’s value is a rational value (a divided by b) interpreted as meters (above sea level):

#include <exiv2/exif.hpp>
#include <exiv2/image.hpp>

int main()
   std::string file("MtEverest.jpg");
   Exiv2::Image::AutoPtr image = Exiv2::ImageFactory::open(file);
   if (image.get())
      // load EXIF data from image file
      Exiv2::ExifData exifData = image->exifData();

      // add a rational value (a divided by b)
      exifData["Exif.GPSInfo.GPSAltitude"] = Exiv2::Rational(884443, 100); // alt = 8844.43 meter
      exifData["Exif.GPSInfo.GPSAltitudeRef"] = int8_t(0); // m.a.s.l.

      // write EXIF data to image file



To print and check the EXIF tags of an image file, we use the exiv2 tool:

exiv2 -PE MtEverest.jpg


Exif.Image.GPSTag                            Long        1  26
Exif.GPSInfo.GPSAltitudeRef                  SLong       1  Above sea level
Exif.GPSInfo.GPSAltitude                     SRational   1  8844.4 m

Here is the geo-tagged image:

MtEverest wikipedia

October 15th 2014 Android Storage | | October 18th 2014 GPS Altitude Correction