Hey guys,
I have a challenge for you ! 
I have a terrain which is a big surface made of triangles. It is not a plane since it has different altitudes, like a real map of the world. See the top part of the image.
I would like to create a “border” around it, to make it look like a small scale model out of concrete. See the bottom part of the image.
Thanks !
You can use Stamp from the Sandbox tools with the offset set to 0.
Note that even if you set the offset to 0, the sides of the stamp won’t be vertical. There is a minimum offset that is larger than 0.
How many edges form the perimeter of the landmass? If it’s less than a few dozen, I would just manually draw vertical edges up from a ground-plane face to each perimeter vertex (using inferencing to locate the lower end of each such edge).
I think you should be able to accomplish this with Joint Push Pull (using vector or extrude?), and then slicing off bottom off with a flat plane. I don’t have time right now to do a test.
I figured it was so close, .025m that the average user could either ignore or know how to fix it. But …
Can it be negative? After all, the earth isn’t flat, so a chunk aught to have the vertical edges converge to the center of the earth rather than flare out. Ok jusdt kidding. Oh, no! Now I may have created an irresistible challenge.
What I love is we can all chat about the existential chunks while at no time actually disturbing the original poster.
Hey Gys,
thanks again for your help !
I did use the Eneroth Terrain Volume tool, which is great and so easy to run, but ran into some issues for some part of my terrain.
Then I tried to Joint Push Pull plugin (from Fredo6, love this guy!), and managed to get what I needed. This last plugin is very fast in computing and has a lot of options, it is great !
Mission accomplished, thanks again and again.
