Compile OpenALPR for Android with NDK

Issue

Is there a way to compile the library OpenALPR (https://github.com/openalpr/openalpr) for Android using NDK (ndk-build)?

Solution

This is a guide to compile the library for android :

Tutorial for compiling OpenALPR for Android devices

[Step 0]

• Download and deploy android-ndk
• Make a symbolic link to android-ndk root folder to /opt

[Step 1]

• Download and Install OpenCV for Android (http://opencv.org/platforms/android.html) (Simply follow the tutorial provided by the OpenCV team)

[Step 2]

• Build the tess-two library (https://github.com/rmtheis/tess-two) (Same thing as OpenCV4Android, follow the build step on the GitHub page)

[Step 3]

• Download and install the Android CMake project (https://code.google.com/p/android-cmake/) You should end up with a toolchain for generating android projects. If you got to choose which compiler to use, I recommend the gcc4.6 as I did not achieve compiling OpenALPR with a toolchain pointing to the gcc4.8 compiler...

• Make a symbolic link to android-toolchain folder inside /opt (ie : sudo ln -s PATH_TO_ANDROID_TOOLCHAIN /opt/android-toolchain). (The android-toolchain folder is generated during the deployment of Android CMake project !)

[Step 4]

• Download the openalpr-master from github (https://github.com/openalpr/openalpr)
• Create a folder "build" inside openalpr-master directory

• Go to the src directory and edit the CMakeLists.txt file :

  • Replace this line : SET(OpenCV_DIR "${CMAKE_SOURCE_DIR}/../libraries/opencv/")
  • with : SET(OpenCV_DIR "path_to_OpenCV4Android/sdk/native/jni")

  Then comment the section for generating alprd (or just remove it) :

  Compile the alprd library on Unix-based OS

  IF (NOT WIN32) ADD_EXECUTABLE( alprd daemon.cpp videobuffer.cpp daemon/beanstalk.c daemon/beanstalk.cc daemon/uuid.cpp )

  TARGET_LINK_LIBRARIES(alprd openalpr support uuid curl log4cplus ${OpenCV_LIBS} ${Tesseract_LIBS} ) ENDIF()

• Open CMake

• Point the Source code to the openalpr-master/src directory
• Point the Build path to the openalpr-master/build directory
• Press the "Configure" button
• Choose "Unix Makefiles" (default) and select "Specify toolchain for cross-compiling" then click "Next"
• Specify the toolchain file to use : if you achieved step 3, it should be located under $ANDROID_CMAKE/toolchain/android.toolchain.cmake (be sure to replace the $ANDROID_CMAKE with its corresponding absolute path)
• Click on finish

There should not be any error but some warnings... it's ok

• Press Generate

[Step 5]

• Go to the build directory and edit this file : misc_utilities/CMakeFiles/benchmark.dir/link.txt : remove the -lpthread option (there should be only one line like this). Save and exit.
• Open a file explorer and go to path_to_tess-two/tess-two/jni/com_googlecode_tesseract_android/src
• Now search every header file (Press the search button and type in ".h" )
• Copy and paste every header file to openalpr-master/src/openalpr/tesseract (you should create this directory first)
• Creates these directories "libraries/tesseract-ocr/api/.libs" in the root path of openalpr-master (mkdir -p libraries/tesseract-ocr/api/.libs)
• Copy and paste path_to_tess-two/tess-two/libs/armeabi-v7a/libtess.so to openalpr-master/libraries/tesseract-ocr/api/.libs/libtesseract.so (be sure to rename it from libtess.so to libtesseract.so !)
• Open a terminal and go to the build folder (openalpr-master/build)
• Do "make"

Everything should compile smoothly. You can find the alpr library in the openalpr-master/src/libs/armeabi-v7a

That's all, let me know your successes and failures, i'll try to help you as best as possible

Answered By - jav974