Ariel’s game engine is Unity. We decided long ago that the project would have a procedurally generated world for every New Game.
We started by exploring different options within Unity. We reached an answer; Gaia Procedural Worlds.
Gaia’s Website: http://www.procedural-worlds.com/gaia/
This tool allowed us to create procedural terrains with masks, which was just what we needed. It is based on Stamps (images/Heightmaps) and it is possible to reach a close level of detail.
We spoke with the creator of the tool regarding one inquiry and he replied very fast. We also saw some of the other tools that he is currently working on, and they seemed great.
Though it is not easy to create a very precise range of probabilities within the procedural generated masks, Gaia contains most of the tool needed for making this possible.
In particular, Ariel needed this creation process to begin during Runtime, and so, we had to write some code ourselves to get this going.
So far, Gaia does not consider fully the Runtime process creation, but I think it will be implemented eventually.
This tool is definitely one to consider if you are planning to implement procedurally generated terrains.