catkin_make编译错误

find_package()查找包时搜索的哪些路径？

find_package()查找包时搜索顺序

一、在工作空间下编译Lego loam的代码，报错如下，

CMake Error at LeGO-LOAM/LeGO-LOAM/CMakeLists.txt: (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:: recipe for target 'cmake_check_build_system' failed
make: *** [cmake_check_build_system] Error 

解决方法：

1. 在terminal中使用 locate 指令查找本机是否有 GTSAMConfig.cmake 或 gtsam-config.cmake 及其所在路径。

2.  echo $PATH  和  echo $GTSAM_DIR  查看环境变量中是否包含上述路径。（一般是不包含的，所以编译时报错）。

3.往环境变量中添加上述路径。至此，一般都可以编译通过。

二、编译pl-slam，报错如下，

  Could not find a package configuration file provided by "G2O" with any of
  the following names:

    G2OConfig.cmake
    g2o-config.cmake

  Add the installation prefix of "G2O" to CMAKE_PREFIX_PATH or set "G2O_DIR"
  to a directory containing one of the above files.  If "G2O" provides a
  separate development package or SDK, be sure it has been installed.

通过locate指令，我在 /usr/local/g2o/lib/cmake/g2o 中找到 g2oConfig.cmake 文件。使用以上方法添加路径后，依然报相同的错误。一番观察后，发现本机文件 g2oConfig.cmake 和报错内容有不相符的地方。于是尝试将本机文件改名，

g2oConfig.cmake --> G2OConfig.cmake

成功解决！

三、在源码包中确实找不到 <PACKAGE>Config.cmake 或者 <package>-config.cmake

有两种方法：1）可能是 package-config 文件，不带cmake后缀；2）下策，自行创建 <PACKAGE>Config.cmake 或者 <package>-config.cmake ；