Hi Adrian,
This finally worked! Although if I may point out, I also had to copy the file hog_bottom_up/gethogs/file_manager.py to the folder .venv/lib64/python3.6/site-packages/gethogs/ so that the program uses this modified file.
A couple of days ago, I had tried to add the csv.field_size_limit argument in file_manager.py that was in the lib64 folder, however this file was overwritten in a subsequent run of OMA. I'm guessing in a new run of OMA, the files in hogs_bottom_up/gethogs/ are installed/copied into lib64, however this did not happen today for some reason and I got the same "too many fields" error. Only after copying the new file_manager.py to lib64 was I able to finish the HOG computation.
Thanks a lot for all your help! Good luck with the further development of the program. I'm a fan and would be using it for a long time ;)