The gpsdings JNI library

Via the gpsdings JNI library, gpsdings exifloc -e can directly use the C++ library libexiv2 to write gps exif information to digital photographs. When you use the exiv2 (or exiftool) standalone executable a new system process is started for each image. In constrast, gpsdingsjni/libexiv2 stays in memory once loaded, and the overhead of creating a new process for each image is avoided. Therefore, in theory, gpsdingsjni/libexiv2 should be faster than the exiv2 executable. However, when the image files are large, disk I/O may come to dominate the processing time so that the speed advantage of gpsdingsjni/libexiv2 over standalone exiv2 becomes minimal (see timing results below).

Installation

Binaries

There are binaries of the library for Linux and Windows on the sf.net download page. The binaries provided have been built using gcc 3.4.4 under Cygwin and gcc 4.0.2 20050901 (prerelease) under SUSE Linux. Put the library file suitable for your platform into the same directory as gpsdings.jar.

Building from source

1. Download the GPSdings jni sources with

   svn export https://svn.code.sf.net/p/gpstools/code/trunk/jni

   and cd to the jni directory.
2. Download the exiv2 source tarball, unpack it, and build it:

   wget http://exiv2.org/exiv2-0.23.tar.gz
   tar xvzf exiv2-0.23.tar.gz
   cd exiv2-0.23
   ./configure --disable-xmp --without-zlib --disable-nls
   make
   cd ..
   

   On Cygwin, you must do

   export CXXFLAGS=-mno-cygwin
   export CFLAGS=-mno-cygwin

   before calling ./configure. I also had to manually edit config.h changing the line

   #define HAVE_SYS_MMAN_H 1

   to

   #undef HAVE_SYS_MMAN_H

   on Cygwin.
3. Install a java sdk if necessary in order to obtain the jni header files.
4. Compile JNIExiv2.cpp from the gpsdingsjni source package. With

   ant

   you can use the provided build scripts (build.xml with win32.properties or unix.properties). You may have to change the locations of the JNI headers, the exiv2 headers (<exiv2dir>/src) as well as the exiv2 library location (<exiv2dir>/src/.libs/libexiv2.a). The build target <gpsdingsjni> must be called gpsdingsjni.dll on Windows and libgpsdingsjni.so on Unix.
5. Copy <gpsdingsjni> to the directory containing the gpsdings.jar file.

Using it

You are ready to use gpsdingsjni/libexiv2 with exifloc. If you copied libgpsdingsjni.so/gpsdingsjni.dll to your library path or to the directory where gpsdings.jar resides you can use exifloc -e without argument. Otherwise you need to specify the path to the library file.