catkin_make编译错误

在工作空间下编译ros的代码包，报错如下，

CMake Error at LeGO-LOAM/LeGO-LOAM/CMakeLists.txt:23 (find_package):
  By not providing "FindGTSAM.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "GTSAM", but
  CMake did not find one.

  Could not find a package configuration file provided by "GTSAM" with any of
  the following names:

    GTSAMConfig.cmake
    gtsam-config.cmake

  Add the installation prefix of "GTSAM" to CMAKE_PREFIX_PATH or set
  "GTSAM_DIR" to a directory containing one of the above files.  If "GTSAM"
  provides a separate development package or SDK, be sure it has been
  installed.


-- Configuring incomplete, errors occurred!
See also "/home/gordon/ros_ws/build/CMakeFiles/CMakeOutput.log".
See also "/home/gordon/ros_ws/build/CMakeFiles/CMakeError.log".
Makefile:13060: recipe for target 'cmake_check_build_system' failed
make: *** [cmake_check_build_system] Error 1

解决方法：

在~/.bashrc中添加环境变量，再source一下就好。

export GTSAM_DIR=/usr/local/gtsam/