编译 cartographer_ros 出现 CMake Error: The following variables are used in this project, but they are set to NOTFOUND.(2021.02.22)
ubuntu版本：20.04
ros版本：noetic
出现如下问题：
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
GMOCK_LIBRARY
linked by target "time_conversion_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "time_conversion_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "msg_conversion_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "msg_conversion_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "metrics_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "metrics_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "configuration_files_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
linked by target "configuration_files_test" in directory /home/mckros/catkin_ws/src/cartographer_ros/cartographer_ros
-- Configuring incomplete, errors occurred!
See also "/home/mckros/catkin_ws/build/CMakeFiles/CMakeOutput.log".
See also "/home/mckros/catkin_ws/build/CMakeFiles/CMakeError.log".
make: *** [Makefile:4520：cmake_check_build_system] 错误 1
Invoking "make cmake_check_build_system" failed
问题提示说：没有找到GMOCK_LIBRARY包
笔者是按照Ubuntu 18.04 安装cartographer方法安装的。
问题解决：
我尝试过使用sudo apt install google-mock安装GMOCK 但是它依旧提示上面的问题。但是我发现我使用 sudo apt install libgmock-dev，他安装了一些包，接下来catkin_make可以发现编译成功
结语
本文也是基于笔者的学习和使用经验总结的，主观性较强，如果有哪些不对的地方或者不明白的地方，欢迎评论区留言交流~
✌Bye
Reference
https://ask.csdn.net/questions/7392012