= Building GDAL with PROJ.4 in Android Studio =

A working project building GDAL with PROJ.4 and bindings as an .aar library easy to use in an Android app:
[https://github.com/paamand/gdal]

= Building GDAL using Android NDK on Linux =

''' Warning! this is still a work in progress! '''


This procedure was developed on a Linux system using Android NDK r5b and is based on
information from this thread: http://groups.google.com/group/android-ndk/browse_thread/thread/9988752f332eff45

== Cross compiling GDAL ==

First, a standalone toolchain is created to make the configure script easier to use. (See android-ndk-r5b/docs/STANDALONE-TOOLCHAIN.html for more details)

{{{
~$ android-ndk-r5b/build/tools/make-standalone-toolchain.sh --platform=android-8 --install-dir=android-8-toolchain
}}}

Next, the toolchain's bin directory is added to the PATH.

{{{
~$ export PATH=$PATH:~/android-8-toolchain/bin/
}}}

From the GDAL source directory, configure for cross compiling and make. (This assumes config.guess and config.sub
where updated. Latest versions can be found here: http://git.savannah.gnu.org/cgit/config.git/tree/)

=== Older GDAL versions (before r21653 - includes 1.8.0) ===
before compiling, patch the source with the patch given at http://trac.osgeo.org/gdal/ticket/3952
=== Newest GDAL versions after r22958 (including 1.9) ===
as below, but  --without-grib is not needed anymore
=== All GDAL versions ===
{{{
gdal$ CFLAGS="-mthumb" CXXFLAGS="-mthumb" LIBS="-lsupc++ -lstdc++" \
      ./configure --host=arm-linux-androideabi --without-grib --prefix=$PROJECT/external/gdal
gdal$ make
gdal$ make install
}}}

The $PROJECT variable contains the path to where you want your Android NDK modules to live.

In $PROJECT/external/gdal, an Android.mk file is created  with the following contents:

{{{
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := gdal
LOCAL_SRC_FILES := lib/libgdal.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include
LOCAL_EXPORT_LDLIBS := -lz
include $(PREBUILT_STATIC_LIBRARY)
}}}

== Using in a JNI library ==

Here's a !HelloGdal app to test the use of the library as part of a JNI component
of an Android project.

In the project's jni directory, hello-jdal.cpp was create with the following contents:

{{{
#include <jni.h>
#include <ogr_api.h>
#include <sstream>

extern "C" {
    JNIEXPORT jstring
    JNICALL Java_org_gdal_HelloGdal_stringFromGDAL(JNIEnv*env, jobject thiz);
}

JNIEXPORT jstring
JNICALL Java_org_gdal_HelloGdal_stringFromGDAL(JNIEnv* env, jobject thiz)
{
    OGRRegisterAll();
    std::ostringstream drivers;
    drivers << "OGR Drivers:\n";
    for (int i = 0; i < OGRGetDriverCount(); ++i)
        drivers << "\t" << OGR_Dr_GetName(OGRGetDriver(i)) << "\n";

    return env->NewStringUTF(drivers.str().c_str());
}
}}}

(Yes, I know, it's called !HelloGdal, yet it lists the OGR drivers. I'll leave it as
an exercise to have the GDAL drivers listed) 

Here's the corresponding Android.mk file:

{{{
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := hello-gdal
LOCAL_SRC_FILES := hello-gdal.cpp
LOCAL_STATIC_LIBRARIES := gdal
include $(BUILD_SHARED_LIBRARY)
$(call import-module,gdal)
}}}

The path to the external GDAL module is set and the library is built using the NDK's build process.

{{{
jni$ export NDK_MODULE_PATH=$PROJECT/external
jni$ $NDK_ROOT/ndk-build
}}}

Finally, the Java portion that uses the JNI library.

{{{
package org.gdal;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;


public class HelloGdal extends Activity {
	
	public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView  tv = new TextView(this);
        tv.setText( stringFromGDAL() );
        setContentView(tv);
    }
	
	public native String stringFromGDAL();
	
	static {
        System.loadLibrary("hello-gdal");
    }
    	
}
}}}

== SWIG bindings ==

You can build and adapt the Java Swig bindings to expose whole GDAL API to the Java portion of an Android application. It needs just one change in typemaps_java.i, see full instructions covering all Android platforms:  [https://github.com/nutiteq/gdal/wiki]