September 01, 2015, 08:40:45 pm
Hi cormac, here's how I'd do it:
1) Create a flat "skirt" around your swimming pool (e.g. 3m wide). The "skirt" should be parallel with the terrain.
2) After re-importing the swimming pool model with the "skirt", assign a Landscape material to the "skirt". This will make the "skirt" blend in with the terrain below it.
3) Lastly, use the Lower terrain tool to carve out the volume inside the swimming pool. The "skirt" ensures that you can't see recessed areas outside the actual swimming pool, so it doesn't matter if the Lower terrain tool isn't 100% accurate.