HELP: CMakeLists.txt for Tesseract with OpenCV

[baqwas]

Hello!

I would like to use Tesseract with OpenCV for a Hello World style sample to understand how to link the respective libraries. The <tesseract/baseapi.h> file is being read, but the link step fails with the following message:

/home/reza/projects/kde/TextExtract/build> make -j8
[ 50%] Linking CXX executable TextExtract
/usr/bin/ld: CMakeFiles/TextExtract.dir/main.cpp.o: in function `main':
/home/reza/projects/kde/TextExtract/main.cpp:54:(.text+0x415): undefined reference to `tesseract::TessBaseAPI::TessBaseAPI()'
/usr/bin/ld: /home/reza/projects/kde/TextExtract/main.cpp:92:(.text+0x587): undefined reference to `tesseract::TessBaseAPI::~TessBaseAPI()'
/usr/bin/ld: /home/reza/projects/kde/TextExtract/main.cpp:92:(.text+0x6da): undefined reference to `tesseract::TessBaseAPI::~TessBaseAPI()'
/usr/bin/ld: CMakeFiles/TextExtract.dir/main.cpp.o: in function `tesseract::TessBaseAPI::Init(char const*, char const*, tesseract::OcrEngineMode)':
/usr/local/include/tesseract/baseapi.h:203:(.text._ZN9tesseract11TessBaseAPI4InitEPKcS2_NS_13OcrEngineModeE[_ZN9tesseract11TessBaseAPI4InitEPKcS2_NS_13OcrEngineModeE]+0x44): undefined reference to `tesseract::TessBaseAPI::Init(char const*, char const*, tesseract::OcrEngineMode, char**, int, std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const*, std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const*, bool)'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/TextExtract.dir/build.make:151: TextExtract] Error 1
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/TextExtract.dir/all] Error 2
make: *** [Makefile:136: all] Error 2
*** Failure: Exit code 2 ***

The current CMakeLists.txt is: (the commented statements didn't work either)

cmake_minimum_required( VERSION 3.5 )
project( TextExtract )
find_package( OpenCV REQUIRED)
find_package( Tesseract REQUIRED )
# set( Tesseract_LIBRARY_DIR "/usr/local/lib/libtesseract" )
include_directories( ${Tesseract_INCLUDE_DIRS} ${OpenCV_INCLUDE_DIRS} )
link_directories( ${Tesseract_LIBRARY_DIR} ${OpenCV_LIBRARY_DIR} )
file( GLOB source_files "*.cpp" )
add_executable( ${PROJECT_NAME} ${source_files} )
target_link_libraries( TextExtract ${OpenCV_LIBS} ${Tesseract_LIBRARY_DIR} )
# target_link_libraries( ${PROJECTCT_NAME} Tesseract::Tesseract OpenCV::opencv_core OpenCV::opencv_imgproc)

Leptonica and Tesseract were built locally from source:

$ pkg-config --libs tesseract
-L/usr/local/lib -ltesseract 
reza@BeUlta:/usr/local/lib$ tesseract --version
tesseract 5.3.4-47-gd5e00
 leptonica-1.84.2
$ which tesseract
/usr/local/bin/tesseract

A code snippet illustrating the initial calls is:

  TessBaseAPI tess; // create Tesseract OCR instance
  if (tess.Init(nullptr, "eng", OEM_DEFAULT)) {
    cerr << "Tesseract initialization failed" << endl;
    return -3;
  }

How do I link the Tesseract library correctly through CMake statements in the CMakeLists.txt file? Thanks.

Regards.

[egorpugin]

opencv + tess
https://github.com/SoftwareNetwork/sw/blob/b0.4.5/test/integrations/cmake/tess/CMakeLists.txt

[baqwas]

Thanks! I will work on installing SW based on your quick response.

I have Tesseract, Leptonica and OpenCV built from source on my desktop. I was hoping that I could leverage these libraries if someone several pay grades above me could help me overcome my elementary mistakes. 🥲

Regards.

[egorpugin]

Feel free to report any issues.