ubuntu18.04安装opencv4.1.2+opencv_contrib4.1.2

下载源文件：

1.opencv4.1.2下载链接：https://github.com/opencv/opencv
2.opencv_contrib4.1.2下载链接：https://github.com/opencv/opencv_contrib

编译

将解压后的opencv_contrib4.1.2放在opencv4.1.2文件夹下，
新建build文件夹：

mkdir build

进入build文件夹：

cd build

编译：

 cmake -D CMAKE_BUILD_TYPE=RELEASE \
       -D CMAKE_INSTALL_PREFIX=/usr/local \
       -D OPENCV_EXTRA_MODULES_PATH=~/Downloads/opencv-4.1.2/opencv_contrib/modules/ \
       -D OPENCV_ENABLE_NONFREE=ON ../

make

安装：

sudo make install

中间遇到的坑

1.opencv下载过程中，如果一直卡在下载ippicv_2019_xxxx处，参考如下博客：
https://blog.csdn.net/heroybc/article/details/101097166
2.make过程中出现fatal error: boostdesc_bgm.i: No such file or directory，为文件缺失导致，参考博客：
https://blog.csdn.net/ninwji/article/details/100798014
3.make过程中出现fatal error: features2d/test/test_detectors_regression.impl.hpp: No such fil，头文件问题，对策详见博客：
https://blog.csdn.net/ninwji/article/details/100798014
4.make过程中出现error: ‘ppf_match_3d’ was not declared in this scope template，查遍了github上的issue，结论是，在build下面执行：
make clean
之后再make，就OK了
5.使用SIFT过程中出现：opencv-4.1.2/opencv_contrib/modules/xfeatures2d/src/sift.cpp:1207: error: (-213:The function/feature is not implemented) This algorithm is patented and is excluded in this configuration; Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function ‘create’
哈哈～
是因为安装opencv时候，cmake时候没有设置OPENCV_ENABLE_NONFREE=ON，重新cmake,make,install去吧