About your questions:
Thank you for your reply.
1. I think ArcGIS Online. I think I found an answer. I got an education license of City Engine and ArcGis Online identity through organisation (my university) Now I can get an access to Terrain Data from City Engine.
2. I don't have ArcGis Desktop ( Thought there is a way to extract mask from OSM and crop the terrain so I don't have extra polygons ?