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.
Any idea ? In my case it is not a rectangle shape for the cutout !