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openalpr-ios

A Ruby script that builds an Xcode project and a universal iOS static library framework for the openalpr library. As of this writing, this project is compatible with the 2.2.x release of OpenALPR and later.

Running the script will:

  • Download the OpenCV 3.0.0 framework binary release and symlink the headers directory so that the OpenALPR code will see them.
  • Download and build universal Tesseract 3.03, Leptonica 1.71, and OpenALPR static library framework bundles from source.
  • Generate a OpenALPR Xcode project

Requirements

  • Mac OS X
  • Ruby 2.1.x, bundler
  • Xcode and command line tools. Tested with Xcode 7.1.
  • curl, tar, unzip, git (seems to be installed by default on OS X)
  • cmake (homebrew | source)
  • autoconf (homebrew | source)

As of this writing, the latest openalpr commit on the master branch was eecd41e097534f84e2669da24d4aed4bf75a1132

Installation

  • Clone this module:

    # git clone [email protected]:twelve17/openalpr-ios.git

  • Install dependencies: bundle install

  • If running Homebrew, unlink existing installs of leptonica and tesseract, as the OpenALPR library will use those instead, which we don't want: brew unlink leptonica tesseract. You can run brew link to re-link them after the install is done.

  • Run bundle exec ./bin/build_frameworks.rb. By default, it will put all the frameworks under a subdirectory called output. You can pass an alternate path with the -d option. Intermediate files are kept under the work subdirectory, including a log called build.log which you can inspect for errors.

Usage

Bitcode

Because the OpenCV binary framework release is compiled without bitcode, the other frameworks built by this script are also built without it, which ultimately means your Xcode project also cannot be built with bitcode enabled. Per this message, it sounds like we want this feature disabled for OpenCV anyway.

To disable bitcode in your project:

  • In Build Settings → Build Options, search for Enable Bitcode and set it to No.

Linking To Frameworks

  • In Xcode, open your project. Then go to Add Files and add all four frameworks (leptonica, opencv, tesseract, openalpr) from the output directory. Use the Copy items if needed option. This should cause the project to add a framework search path to the project's build settings (e.g. $(PROJECT_DIR)).
  • Ensure that all four frameworks are included in the Link Binary With Libraries build phase.
  • The alpr library requires a config file (openalpr.conf) and a data folder (runtime_data), both of which are included in the framework, but must be copied to the application resources:
    • Select your project on the project navigator, then, on the main pane, go to Targets → <Your Project> → Build Phases → Copy Bundle Resources, and click on the +.
    • Select Add Other...
    • Browse into the openalpr.framework bundle, and command-select both runtime_data and openalpr.conf. Unselect Copy items if needed and select Create folder references.

AlprSample App

You can use the AlprSample app included in this project to test your installation. It has one view that simply presents a fixed (pre-selected) license plate image, and a table view below it showing scanned plate values for that image.

To run the app, you will need to build the frameworks with build_frameworks.rb. Then, in Xcode, open the project and follow these steps:

  1. Find a plate image file you wish to test with and add it to the project.
  2. Edit ViewController.mm and change the value of plateFilename to the name of the file you added in step 1, e.g. NSString *plateFilename = @"license_plate.jpg";
  3. Link the project to the dependency frameworks and add the required resources per the "Linking To Frameworks" section above.
  4. Run the app! The library should work in a simulator.

Misc Notes

Dynamic Library?

I initially attempted to build dynamic libraries, since they are supported as of iOS 9. It required me to update the rpath of the dynamic libraries. Then the frameworks must be embedded into the application. However, even after doing that, I ran into odd run-time errors where the libopenalpr.dylib library could not load the statedetection library. PRs welcome!

AlprSample Creation

Steps for creating the app are kept here for posterity.

  • Create New Project
    • iOS → Application → Single View Application
    • Product Name: AlprSample
  • You should end up with a project which contains, among other things, a ViewController.h and ViewController.m class. Rename the .m class to ViewController.mm (two m's). This causes Xcode to compile the class as "Objective-C++", which we need, as the openalpr code is in C++.
  • Disable bitcode per the "Bitcode" section above.
  • Link the project to the dependency frameworks and add the required resources per the "Linking To Frameworks" section above.

Tips

  • Viewing iOS device logs

  • Viewing symbols in library: nm -gUj openalpr.framework/Libraries/libopenalpr-static.a | c++filt

  • Inspecting the Simulator logs: tail -f ~/Library/Logs/CoreSimulator/*.log

  • clean up temporary Xcode items

     rm -rf "$(getconf DARWIN_USER_CACHE_DIR)/org.llvm.clang/ModuleCache"
 rm -rf ~/Library/Developer/Xcode/DerivedData
 rm -rf ~/Library/Caches/com.apple.dt.Xcode

Credits