ubuntu14.04,之前已经安装了OpenCV2（默认的安装路径是/usr/local）,现在需要安装OpenCV3.2，但是又不想将opencv2删除
1.首先，下载好opencv3.2(download: https://github.com/opencv/opencv/archive/3.2.0.zip)后，将源码解压
2.修改CMakeLists.txt文件
将默认的安装路径：/usr/local修改为你要安装的路径
set(CMAKE_INSTALL_PREFIX "/home/alan/slambook/opencv3" CACHE PATH "Installation Directory")
3.编译
cmake ..
make
make install
在指定安装的路径下找到对应的头文件和库
4.
如何在工程中加入opencv3.2的库和头文件。
这里需要改变一下，否则很容易链接到位于/usr/local下的opencv2。在工程文件中的CMakeLists.txt加上：
set(OpenCV_DIR "/home/ubuntu/src/opencv-3.1.0/build")
来重新制定opencv的安装路径，因为安装opencv2时已经生成了系统变量OpenCV_DIR = /usr/local/share/opencv,所以需要用set来改变这个变量的值，新的路径为与文件OpencvConfig.cmake路径相同。
cmake_minimum_required( VERSION 2.8 )
project( loop_closure )
set( CMAKE_BUILD_TYPE "Release" )
set( CMAKE_CXX_FLAGS "-std=c++11 -O3" )
# opencv
set(OpenCV_DIR "/home/lzp/software/opencv-3.2.0/build")
find_package(OpenCV REQUIRED )
include_directories( ${OpenCV_INCLUDE_DIRS} )
message(STATUS " version: ${OpenCV_VERSION}")
# dbow3
# dbow3 is a simple lib so I assume you installed it in default directory
set( DBoW3_INCLUDE_DIRS "/usr/local/include" )
set( DBoW3_LIBS "/usr/local/lib/libDBoW3.a" )
add_executable( feature_training feature_training.cpp )
target_link_libraries( feature_training ${OpenCV_LIBS} ${DBoW3_LIBS} )
add_executable( loop_closure loop_closure.cpp )
target_link_libraries( loop_closure ${OpenCV_LIBS} ${DBoW3_LIBS} )
add_executable( gen_vocab gen_vocab_large.cpp )
target_link_libraries( gen_vocab ${OpenCV_LIBS} ${DBoW3_LIBS} )
