Here is a short tutorial showing you how to paint your terrain in Twinmotion within 1 minutes:
Twinmotion plugin to Revit 2014 / 2015 / 2016 / 2017 is available online: https://twinmotion.abvent.com/downloads/
https://www.youtube.com/watch?time_continue=16&v=hvZsPSP8cEs
Twinmotion / Abvent