Linking local library in c++ (macOS High Sierra) - c++

Question

I'm trying to link a library called apriltags to my c++ project. I've downloaded the source files, placed them in my project and set up the CMakeLists.txt such that the imports in my classes work fine. However, there is a referencing problem, such that I get the following error when using building with:
$ /Applications/CLion.app/Contents/bin/cmake/bin/cmake --build "/Users/petter/Desktop/MSc Project/autonomous-car/cmake-build-debug" --
target autonomous_car -- -j 2
Error:
[ 50%] Linking CXX executable bin/autonomous_car
Undefined symbols for architecture x86_64:
"AprilTags::TagDetector::extractTags(cv::Mat const&)", referenced from:
_main in main.cpp.o
"AprilTags::TagFamily::TagFamily(AprilTags::TagCodes const&)", referenced from:
AprilTags::TagDetector::TagDetector(AprilTags::TagCodes const&) in main.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[3]: *** [bin/autonomous_car] Error 1
make[2]: *** [CMakeFiles/autonomous_car.dir/all] Error 2
make[1]: *** [CMakeFiles/autonomous_car.dir/rule] Error 2
make: *** [autonomous_car] Error 2
Here is my code:
#include <iostream>
#include <cstring>
#include <vector>
#include <sys/time.h>
#include <AprilTags/TagDetector.h>
#include <AprilTags/Tag36h11.h>
#include <eigen3/Eigen/Dense>
using namespace AprilTags;
using namespace cv;
int main() {
VideoCapture cap(0); // open the default camera
if (!cap.isOpened()) // check if we succeeded
return -1;
namedWindow("view", 1);
TagCodes tag_codes = tagCodes36h11;
TagDetector* detector = NULL;
detector = new TagDetector(tag_codes);
for (;;) {
Mat frame;
cap >> frame; // get a new frame from camera
vector<TagDetection> det = detector->extractTags(frame);
imshow("view", frame);
if (waitKey(30) >= 0) break;
}
return 0;
}`
And here is my CMakeLists.txt:
cmake_minimum_required(VERSION 3.10)
project(autonomous_car)
set(SOURCE_FILES main.cpp )
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
add_executable(autonomous_car ${SOURCE_FILES})
add_library(apriltags ${SOURCE_FILES})
find_package(OpenCV REQUIRED)
find_package(Sdl2 REQUIRED)
find_package(PkgConfig)
pkg_check_modules(EIGEN3 REQUIRED eigen3)
include_directories(${EIGEN3_INCLUDE_DIRS})
target_link_libraries(apriltags)
target_link_libraries(autonomous_car ${OpenCV_LIBS})
target_link_libraries(autonomous_car ${Eigen_LIBS})
target_link_libraries(autonomous_car ${Sdl2_LIBS})
include_directories(apriltags . )
include_directories(${Eigen_INCLUDE_DIRS})
include_directories(${OpenCV_INCLUDE_DIRS})
include_directories(${Sdl2_INCLUDE_DIRS})
Project structure:
project structure