i have a terrain that looks like a height map
i have also made a tunnel that looks like the one in oasis, but i dont know how to cut my terrain so that the ASE will fit.
i have tried to do it with 3 point clipping but i dont know, doesnt come out right.
and i hear csg substract is terrible brushwise what do i do?
how was the one in oasis done?
Have a look at This tutorlial by Ifurita
It explains how to cut out terrain for buildings, you’ll have to caulk around your .ase tunnel so it “feels” like solid ground though.
Well, for the parts of the terrain where the tunnel is under the ground/mountains you could simply select the brushes that are visible from inside the tunnel, and then resize them up, drag the bottom to the top, until they are no longer in the tunnel.
Make sure you don’t accidently go too far. You went too far if your brushes start to deform or become smaller.
Hard to explain but you will get what i mean if you try it.
For the entrances it will be just 2 or 3 point clipping i guess yeah… don’t think there’s any other way except normal vertex editing.
I used this tutorial to make mountains and anything connected with rocks…
http://www.simonoc.com/pages/articles/rockdetail1_1.htm
I also make tunells with this method…
There is a part of this article that tells you how to connect one type of brushes to another one…
My idea would be to cut out two wholes in your terrain so that your tunnel would connect them… and then connect the tunnel brushes with the terrain brushes using this method… than it should look as if you made it from scratch…
Have fun… Sometimes it takes a bit to make it look great but isn’t mapping all about that? 
Part of what I made
