Tesseract 4.0 is currently not as easy to install on all systems as earlier versions. Version 4.0 is not officially released, so these difficulties are understandable.
- Missing eng.traineddata and other training files
The language files are specific to the Tesseract version. For Tesseract 4.0+, you can use either files from tessdata_best, as suggested here. The tessdata_fast files will also work.
For Tesseract versions 3.04+, you need to use the files from tessdata
These files can be put into the default search locations (e.g., /usr/local/share) or Tesseract can be told where to find them with the tessdata flag.
- aspell is suggested (not a dependency)
R CMD BUILD said I was missing aspell, so I got from omegahat.net You might need to apply this fix
On Ubuntu, we use clang ./configure CXX=clang++ CC=clang
The option --disable-openmp doesn't disable it fully and we get an error when compiling the code in the lstm/ directory.
So we install libopenmp-dev.
On Ubuntu with clang 3.8, we added the std:: prefix in lstm/lstmrecognizer.cpp std::isnan() in LabelsViaThreshold() (See https://stackoverflow.com/questions/39130040/cmath-hides-isnan-in-math-h-in-c14-c11)
problems after install of tesseract 4.0.0-beta.4 from source
- !strcmp(locale, "C"):Error:Assert failed
Originates with this line in baseapi.cpp: ASSERT_HOST(!strcmp(locale, C)); The error is due to a recent change in tesseract source: https://github.com/tesseract-ocr/tesseract/commit/3292484f67af8bdda23aa5e510918d0115785291#diff-903b81bdfe923135ee1d03800c400ed8 See tesseract-ocr/tesseract#1670
Since this is an unresolved issue, for now I just undid that change in the tesseract code (in src/api/baseapi.cpp)