Deploy to hardware tutorial

In your deploy to hardware tutorial on youtube, you demonstrated how to use the thresholding application. I am stuck as it says the output of my function is in boolean form and not double as required. I tried changing it with a line of code but it didnt work, may I have the solution? Furthermore, I am not participating in the competition but completing some aspects as my individual final year project. Is it possible to have any sample working line follower drones as I am doing this all on my own?