How can you keep a Geometry Nodes displaced plane's edges at location 0 on the Z axis?

Question

So, within a Geometry Nodes setup I'm using a noise texture to create a procedural landscape on a Grid Primitive as explained in many YouTube videos.

The node tree I use works by using the noise texture fed into the Offset socket on a Set Position node (various other nodes in the node tree e.g. Math nodes etc).

I'm trying to figure out how to select the perimeter of the Grid Primitive and prevent it from moving on the Z axis i.e. pin the perimeter down using the Geometry Nodes setup. It would be even better if I could apply some sort of adjustable falloff from the perimeter edges etc.?

I can't find anything at all to help me with this?

Answer 1

you can use edge neighbors node to select inside faces of mesh, not the border.

(blender 3.6.1)

Answer 2

You have several possibilities here...

One possibility would be to combine the noise texture with a gradient texture, and to define its effect and range with Map Range:

Another possibility would be, if you really need the exact distance to the outer edges, to combine this distance with the noise texture using Geometry Proximity:

_{(Blender 3.6+)}