今天编译cartographer遇到问题：
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/dh-ubuntu/carto_ws/src/cartographer_ros/cartographer_ros linked by target "configuration_files_test" in directory /home/dh-ubuntu/carto_ws/src/cartographer_ros/cartographer_ros linked by target "msg_conversion_test" in directory /home/dh-ubuntu/carto_ws/src/cartographer_ros/cartographer_ros linked by target "metrics_test" in directory /home/dh-ubuntu/carto_ws/src/cartographer_ros/cartographer_ros -- Configuring incomplete, errors occurred!
根据网上的提示，安装sudo apt install libgmock-dev，一直失败。
最后通过重新安装gtest包，解决：
下载gtest，release-1.8.0
git clone https://github.com/google/googletest
如果下载太慢：
git clone https://gitee.com/anynone/google-googletest.git
gtest编译
cd googletest
生成Makefile文件(先安装cmake，brew install cmake)，继续输入命令编译:
cmake CMakeLists.txt
执行make，生成两个静态库：libgtest.a libgtest_main.a
make
最后将lib中的文件全部拷贝到 /usr/lib
