Setting Up OpenCV

I was trying to use the Tensorflow’s newly released Object Detection API on my webcam. I realised I couldn’t open webcam, OpenCV which was bundled with ROS was throwing all sorts of errors, I Googled and tried many hacky solution but all in vain.

Now that my end sems were over I decided to install it fresh.

This site : https://www.learnopencv.com/install-opencv3-on-ubuntu/ is a great walktrough through the installation process. It’s absolutely complete.

There the author had used a virtualenv to work on.

Now I had done this for both Python2 and Python3 ! Now when I opened my webcam in Python2 it worked like charm, but as soon as I changed the ‘2’ to ‘3’ it again crashed !!

Now I decided to follow the instructions exaclty and created a virtual env ! Then I followed the steps and it worked !!

Now why my normal installation wasn’t working ??

Using

find /usr/local/lib/ -type f -name "cv2*.so"

I found that the installed OpenCV for Python3 was at

/usr/local/lib/python3.5/dist-packages/cv2.cpython-35m-x86_64-linux-gnu.so

But when I inspected what .so file python was importing I found it was trying to use the .so file at

/home/sangeet/.local/lib/python3.5/site-packages/cv2/cv2.cpython-35m-x86_64-linux-gnu.so

Then I tried creating a symlink between the two, but since both the files had the same name it couldn’t be done.

Then out of hope I copied the file from

/usr/local/lib/python3.5/dist-packages/cv2.cpython-35m-x86_64-linux-gnu.so

to

/home/sangeet/.local/lib/python3.5/site-packages/cv2/cv2.cpython-35m-x86_64-linux-gnu.so

and simply overwrite it !!

Pheww.. It worked !!