Linking problems with dlib: recompile with -fPIC - c++

Question

I would like to use this ROS package which relies on dlib. I compile with catkin build, but I get this error in linking I guess:
/usr/bin/ld: /usr/lib/libdlib.a(threads_kernel_shared.o): relocation R_X86_64_PC32 against symbol `_ZN4dlib21threads_kernel_shared14thread_starterEPv' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Bad value
collect2: error: ld returned 1 exit status
make[2]: *** [/home/alberto/tiago_dual_public_ws/devel/.private/gazr/lib/libgazr.so] Error 1
make[1]: *** [CMakeFiles/gazr.dir/all] Error 2
make: *** [all] Error 2
I have installed dlib using sudo apt-get install libdlib-dev on my Ubuntu 18.05 (ROS Melodic) machine. How can I solve this problem? Documentation of dlib and the repo instruction does not help me a lot.
Thanks in advance.

Answer 1

I found 2 possible solution to the problem.
Installing dlib with sudo apt-get install libdlib-dev
In this case you should link dlib to your library target like target_link_libraries(gazr dlib ${OpenCV_LIBRARIES})
Rememberto use find_package(dlib REQUIRED)
Installing dlib from source
It's also possible to use directly the dlib source file. In this case you need to add the dlib source directory to the project using add_subdirectory(your_path/dlib dlib) and add it to the library target_link_libraries(gazr dlib ${OpenCV_LIBRARIES}).
ATTENTION: In this case you shall not use find_package(dlib REQUIRED)
Hope this is helpful!