Procedural Socket-Generation for Landscape

Hey guys,

for a german doc-series about east-germany, I need to create a fly over a map (Link to Google-Drive).

To achieve this I imported a hightmaptile into Houdini, eroded it, textured it and than imported it to Unreal. To create the clipping effect at the borders I used a 3D Box Mask.

Now I want to build a socket under the landscape like the one in the EXAMPLE IMAGE. Do you guys have any hints on how to achieve an effect like that? It should of course behave according to the movement of the landscape.

Best Regard,