為什麼pkg-config –modversion opencv4 顯示 Package opencv-4.*.* was not found in the pkg-config search path ?

為什麼pkg-config –modversion opencv4 顯示 Package opencv-4.*.* was not found in the pkg-config search path ?
原因 :
OpenCV 4 預設不使用 pkg-config .
在編譯時需加入
-D OPENCV_GENERATE_PKGCONFIG=ON