SLAM14讲，Sophus使用，Find_Package()无法定位

ch4的示例代码，拿出来测试，总是出现如下错误：

SLAM/demo/ch4/src/useSophus.cpp:5:10: fatal error: sophus/se3.hpp: 没有那个文件或目录
 #include "sophus/se3.hpp"
          ^~~~~~~~~~~~~~~~

这时CMakeLists.txt中是这样的：

#需要使用find_package命令找到它
find_package(Sophus REQUIRED)
include_directories(${Sophus_INCLUDE_DIRS})

我想显示${Sophus_INCLUDE_DIRS}，于是加了一句：MESSAGE()如下所示：

#需要使用find_package命令找到它
find_package(Sophus REQUIRED)
include_directories(${Sophus_INCLUDE_DIRS})

message(STATUS "Include_directories: " ${Sophus_INCLUDE_DIRS})

之后Cmake结果是：

xj@xj-MRC-WX0:~/SLAM/demo/ch4/build$ cmake ..
-- Include_directories: 
-- Configuring done
-- Generating done
-- Build files have been written to: /home/xj/SLAM/demo/ch4/build

可见，根本就没有正确的include路径，于是只能指定绝对路径了，完整的CMakeLists.txt为：

#需要使用find_package命令找到它
#find_package(Sophus REQUIRED)
#include_directories(${Sophus_INCLUDE_DIRS})
include_directories("/home/xj/SLAM/3rdparty/Sophus/sophus")
message(STATUS "Include_directories: " ${Sophus_INCLUDE_DIRS})

# Eigen
include_directories("/usr/include/eigen3")
add_executable(useSophus useSophus.cpp)

注意，因为指定到了..Sophus/sophus,所以源码中的useSophus.cpp也要改一下：

#include "sophus/se3.hpp"

改成 ：

#include "se3.hpp"

结果就没有问题了：

xj@xj-MRC-WX0:~/SLAM/demo/ch4/build$ make
Scanning dependencies of target useSophus
[ 50%] Building CXX object src/CMakeFiles/useSophus.dir/useSophus.cpp.o
[100%] Linking CXX executable useSophus
[100%] Built target useSophus

总结一下：之前以为是Sophus没有编译（build）好，各种试，原来只是Include没有find,为什么？先不深究了，赶进度测试学习。