Install openCV with CUDA toolkit 8.0 - opencv

Question

I'm trying to install Opencv 3.2.0 and Nvidia CUDA toolkit 8.0 on Ubuntu 16.04 but I can't configure them together. I get the following error when I try to make project using both:
CMake Error at /usr/share/cmake-3.5/Modules/FindPackageHandleStandardArgs.cmake:148 (message):
Could NOT find CUDA: Found unsuitable version "8.0", but required is exact
version "7.5" (found /usr/local/cuda)
Call Stack (most recent call first):
/usr/share/cmake-3.5/Modules/FindPackageHandleStandardArgs.cmake:386 (_FPHSA_FAILURE_MESSAGE)
/usr/share/cmake-3.5/Modules/FindCUDA.cmake:949 (find_package_handle_standard_args)
/usr/local/share/OpenCV/OpenCVConfig.cmake:86 (find_package)
/usr/local/share/OpenCV/OpenCVConfig.cmake:105 (find_host_package)
CMakeLists.txt:10 (find_package)
-- Configuring incomplete, errors occurred!
I have tried installing cuda toolkit 7.5 but its not compatible with ubuntu 16.04 I believe. I'm really clueless now, I hope someone can help with this.
Thanks

Answer 1

so I solved this issue by managing to install toolkit 7.5. Here is how I did it:
Updated nvidia driver for my Operating System
Download cuda toolkit 7.5 and extract it to a folder
$ mkdir ~/Downloads/NVIDIA_TOOLKIT
$ cd ~/Downloads
$ ./cuda_7.5.18_linux.run -extract=~/Downloads/NVIDIA_TOOLKIT;
go to the virtual console by pressing Ctrl + Alt + F1 and turn off
lightdm service
$ sudo service lightdm stop
cd to downloads and install the extracted toolkit and samples
$ cd ~/Downloads/NVIDIA_TOOLKIT
$ sudo ./cuda-linux64-rel-6.0.37-18176142.run
$ sudo ./cuda-samples-linux-6.0.37-18176142.run
Set environment variables in .bashrc file
$ PATH=/usr/local/cuda-7.5/bin
$ LD_LIBRARY_PATH=/usr/local/cuda-7.5/lib64
Turn back on the lightdm service
$ sudo service lightdm start
Reboot and you should be able to use the nvcc compiler
For openCV you will have to downgrade your gcc/ g++ compiler to 4.9 since it is not yet compatible with the higher versions