Is the project you are building fixed or do you use cmake to generate it?
If its fixed, somewhere in your configuration the path to
C:\workspace\opencv3\build\install\include\
will be specified, probably as
%OPENCV_DIR%\..\..\include
If you are unable to find it I would suggest manually adding
C:\workspace\opencv3\build\install\bin\
and
C:\workspace\opencv3\build\install\lib\
to your user path. That way the executable can find the opencv dll’s when you run it and if you have another project that autodetects the libs using a cmake or other script they will be on the path.
Then set OPENCV_DIR to
C:\workspace\opencv3\build\install\x64\vc15
I know it doesn’t exist but the headers should be found.
Then you will probably find that your lib’s won’t be detected as they are probably also relative to OPENCV_DIR.