编译时错误如下：
/usr/bin/ld: warning: libopencv_imgcodecs.so.3.2, needed by /home/thinkpad/Desktop/ubuntu18-ros/mavros_ws/devel/lib/libapriltag_ros_single_image_detector.so, may conflict with libopencv_imgcodecs.so.3.3
/usr/bin/ld: warning: libopencv_core.so.3.3, needed by /usr/local/lib/libopencv_imgcodecs.so.3.3.1, may conflict with libopencv_core.so.3.2

这是同时存在两个版本，链接时不知道该找哪个．3.3是自己编译的，3.2是系统自带的
查看系统使用的opencv版本

pkg-config --modversion opencv

在find_package(OpenCV REQUIRED)中添加opencv的版本find_package(OpenCV 3.3 REQUIRED)

undefined reference to `cv::Mat::Mat()’
在可执行文件链接库中加入opencv库即可，即加入 ${OpenCV_LIBS}