【OpenCV】多版本那是interesting

OpenCV在使用时的问题

摘要

如果多版本安装OpenCV，切勿默认安装，务必每安装一个版本都新建一个目录，这样就会少很多问题。但是安装ROS会不知不觉的将自带的OpenCV安装到默认路径。一样会导致冲突。这时候最好的解决办法还没找到，所以最好的办法就是用ROS自带的OpenCV，虽然有警告，但是可以用呀！

背景

1. 安装Ubuntu20.04对应的ROS，顺带安装个OpenCV4.2.0安装到默认路径(相当讨厌，也有优势)；
2. 安装了OpenCV4.8.0 到指定目录，用于ORB-SLAM3，顺利使用没有啥问题，未见冲突；
3. 配置OpenCV3.2.0和VINS-fusion，编译通过，但是显示有警告。最可怕的是运行失败（直接段错误）可以使用gdb调试查看原因，原因是，在链接库文件时它偷偷摸摸链接到OpenCV4.2.0。让人担心的警告直接发生了。可供参考
4. 解决方法，就是修改找opencv直接链接到ROS自带的4.2.0，编译VINS-fusion通过，但是显示有警告。可是它真的没有偷偷摸摸链接到其他库。勉强可用！！！

关于第3条，警告信息如下，这几个可能conflict

 	/usr/local/opencv3.2.0/lib/libopencv_core.so.3.2
    /usr/local/opencv3.2.0/lib/libopencv_imgcodecs.so.3.2
    /usr/local/opencv3.2.0/lib/libopencv_calib3d.so.3.2
    /usr/lib/x86_64-linux-gnu/libopencv_core.so.4.2
    /usr/lib/x86_64-linux-gnu/libopencv_imgcodecs.so.4.2
    # /usr/local/opencv3.2.0/lib/libboost_filesystem.so.1.71.0
    /usr/local/opencv3.2.0/lib/libopencv_features2d.so.3.2
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关于第4条，警告信息如下：

...
[ 97%] Linking CXX executable /home/pf/VINSfusionFix/devel/lib/vins/kitti_gps_test
[ 98%] Linking CXX executable /home/pf/VINSfusionFix/devel/lib/vins/kitti_odom_test
/usr/bin/ld: warning: libopencv_calib3d.so.4.2, needed by /home/pf/VINSfusionFix/devel/lib/libvins_lib.so, may conflict with libopencv_calib3d.so.3.2
/usr/bin/ld: warning: libopencv_imgcodecs.so.3.2, needed by /home/pf/VINSfusionFix/devel/lib/libvins_lib.so, may conflict with libopencv_imgcodecs.so.4.2
/usr/bin/ld: warning: libopencv_core.so.3.2, needed by /usr/local/opencv3.2.0/lib/libopencv_calib3d.so.3.2, may conflict with libopencv_core.so.4.2
/usr/bin/ld: warning: libopencv_calib3d.so.4.2, needed by /home/pf/VINSfusionFix/devel/lib/libvins_lib.so, may conflict with libopencv_calib3d.so.3.2
/usr/bin/ld: warning: libopencv_imgcodecs.so.3.2, needed by /home/pf/VINSfusionFix/devel/lib/libvins_lib.so, may conflict with libopencv_imgcodecs.so.4.2
/usr/bin/ld: warning: libopencv_core.so.3.2, needed by /usr/local/opencv3.2.0/lib/libopencv_calib3d.so.3.2, may conflict with libopencv_core.so.4.2
[ 98%] Built target kitti_gps_test
[ 98%] Built target kitti_odom_test
[100%] Linking CXX executable /home/pf/VINSfusionFix/devel/lib/vins/vins_node
/usr/bin/ld: warning: libopencv_calib3d.so.4.2, needed by /home/pf/VINSfusionFix/devel/lib/libvins_lib.so, may conflict with libopencv_calib3d.so.3.2
/usr/bin/ld: warning: libopencv_core.so.3.2, needed by /usr/local/opencv3.2.0/lib/libopencv_calib3d.so.3.2, may conflict with libopencv_core.so.4.2
[100%] Built target vins_node
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重点解释说明第4条

解决方法，就是修改找opencv直接链接到ROS自带的4.2.0，编译VINS-fusion通过，但是显示有警告。可是它真的没有偷偷摸摸链接到其他库。勉强可用！！！

修改一些报错

ROS noetic版本中的OpenCV4.2和VINS-fusion中需要使用的OpenCV3冲突，修改以兼容OpenCV4。幸运的是发现不用修改代码中不兼容的变量，可以直接添加缺失的头文件即可：

如下：

• 在camera_models包中的头文件Chessboard.h中添加

#include 
#include 
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• 在camera_models包中的头文件CameraCalibration.h、pose_graph包中的头文件pose_graph.h和keyframe.h、BRIEF.h中添加

#include 
#include 
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• 若vins_estiamtor包中报错，将头文件替换为

// #include 
// #include 
#include 
#include 
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找OpenCV

重点是找默认的opencv ，

• 你以为直接确定版本可以找到ROS对应的4.2.0，可是它找不到

find_package(OpenCV 4.2 REQUIRED)
message(WARNING "OpenCV_VERSION: ${OpenCV_VERSION}")

#输出：
#CMake Warning at CMakeLists.txt:21 (message):
#OpenCV_VERSION: 4.8.0
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• 你以为不加版本直接找可以找到ROS对应的4.2.0，可是它也找不到，不仅找不到，它找上一次有版本的opencv（自己体会这句话）

find_package(OpenCV REQUIRED)
message(WARNING "OpenCV_VERSION: ${OpenCV_VERSION}")

#输出：
#CMake Warning at CMakeLists.txt:21 (message):
#OpenCV_VERSION: 4.8.0
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• 正确的方法 去找ROS对应的4.2.0对应的文件OpenCVConfig.cmake 然后找到路径，这就可以了。
• cmake编译原理是需要CMakeLists.txt找到 .cmake 文件，就在那几个目录下面，
  1. /usr/share/OpenCV/
  2. /usr/lib/x86_64-linux-gnu/cmake/opencv4/
  3. …

set(OpenCV_DIR /usr/lib/x86_64-linux-gnu/cmake/opencv4/)
find_package(OpenCV REQUIRED)
# -- Found OpenCV: /usr (found version "4.2.0")
# OPENCV VERSION: 4.2.0
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find_package(catkin REQUIRED COMPONENTS
	OpenCV
	)
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pf@pf-NUC12WSKi7:~/VINSfusionFix$ catkin_make
Base path: /home/pf/VINSfusionFix
Source space: /home/pf/VINSfusionFix/src
Build space: /home/pf/VINSfusionFix/build
Devel space: /home/pf/VINSfusionFix/devel
Install space: /home/pf/VINSfusionFix/install
####
#### Running command: "make cmake_check_build_system" in "/home/pf/VINSfusionFix/build"
####
####
#### Running command: "make -j16 -l16" in "/home/pf/VINSfusionFix/build"
####
[  5%] Built target libGeographiccc
[ 24%] Built target camera_models
[ 45%] Built target Calibrations
[ 49%] Built target global_fusion_node
[ 68%] Built target loop_fusion_node
[ 91%] Built target vins_lib
[ 97%] Built target kitti_gps_test
[ 97%] Built target kitti_odom_test
[100%] Built target vins_node

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