Correction in OpenCV's default CMAKE search Path for OpenBLAS Library on Ubuntu-64bit Machines [Solution]

[abhiTronix]

System information (version)

• OpenCV => 4.0.0 - pre(Latest - master)
• Operating System / Platform => Ubuntu 18.04 64 Bit
• Compiler => GCC 7.3.0 (Default)

Detailed description

Hello there,

I found a simple & straightforward solution to the problems of OpenBLAS Library not being identified properly on Ubuntu machine (64-bit) in CMAKE configuring step, also may work on other Linux Distros :)

Completely Solves: #9953

Installation:

OpenBLAS can installed from respected default repository with the following command:

sudo apt install libopenblas-dev, libopenblas-base

Whereas LAPACK Library is little trickier to install, as OpenBLAS doesn't provide Lapacke header file(i cannot find the lapacke.h header fie ), Therefore I ought to install LAPACK Library instead, which works absolutely fine:

sudo apt install liblapacke-dev

sudo ln -s /usr/include/lapacke.h /usr/include/x86_64-linux-gnu # corrected path for the library 

Setting Correct Path:

So, The only thing left is setting Correct Default Search Path for Include and Libs Directory of OpenBLAS Library which is as below :

• Open_BLAS_INCLUDE_SEARCH_PATHS path: /usr/include/x86_64-linux-gnu
• Open_BLAS_LIB_SEARCH_PATHS path: /usr/lib/x86_64-linux-gnu

Appending these respective additional Paths in OpenCVFindOpenBLAS.cmake :

opencv/cmake/OpenCVFindOpenBLAS.cmake

Line 46 in eb981cc

SET(Open_BLAS_INCLUDE_SEARCH_PATHS

and

opencv/cmake/OpenCVFindOpenBLAS.cmake

Line 58 in eb981cc

SET(Open_BLAS_LIB_SEARCH_PATHS

Completely solves the issue without altering any additional file in OpenCV. Kindly Add these additional paths to the above-mentioned file :)

Results:

Before appending path:

-- Could not find OpenBLAS include. Turning OpenBLAS_FOUND off
-- Could not find OpenBLAS lib. Turning OpenBLAS_FOUND off
-- Could NOT find Atlas (missing: Atlas_CBLAS_LIBRARY Atlas_BLAS_LIBRARY) 
.
.
-- LAPACK(LAPACK/Generic): LAPACK_LIBRARIES: /usr/lib/x86_64-linux-gnu/libopenblas.so;/usr/lib/x86_64-linux-gnu/libopenblas.so
-- LAPACK(LAPACK/Generic): Support is enabled.

After appending path:

-- Found OpenBLAS libraries: /usr/lib/x86_64-linux-gnu/libopenblas.so
-- Found OpenBLAS include: /usr/include/x86_64-linux-gnu
-- LAPACK(OpenBLAS): LAPACK_LIBRARIES: /usr/lib/x86_64-linux-gnu/libopenblas.so
-- LAPACK(OpenBLAS): Support is enabled.

After Correction, OpenBLAS library configured correctly with OpenCV on my system, Cheers.

[alalek]

Such workarounds should be added as a comment into original issue.

[abhiTronix]

@alalek Actually the solution is Altering OpenCVFindOpenBLAS.cmake in the source and adding additional paths. That's why I opened it as an issue. Can you please add them and crosscheck the results?