Known OpenCV issues

[tcies]

Newer versions of OpenCV break some parts of the build.

Problem: "SURF" is not a member of "cv" in dbow2

Yay interface changes... thankfully we don't need SURF, this was just needed in the old version of DBoW2 for their demo. Simply comment out https://github.com/uzh-rpg/DBoW2/blob/master/CMakeLists.txt#L22-L27

OpenCV linking issues

Ideally, you would only have one OpenCV version on your PC. Consider:

• Removing all unused OpenCV versions from /usr/local or apt uninstalling them
• If you use python, only install OpenCV in virtualenvs that are not active during the build of dslam_open

Thanks Benchun Zhou from KIT for feedback on these issues.

[benchun123]

Thanks so much! --Benchun zhou