How to add a ground for a model that is used as a displacement modifier? How would anybody go if you have a model and you use it as a displacement texture, but the ground to be separated from the model (not literaly separated, but to distinguish the ground from the model)? Maybe the boolean can solve the problem, but of big curiosity, what are some of the ways and approaches of doing that?

I'm aiming for this kind of result -
use an image to control the displacement:




Generate an image that controls an alpha channel for texturing



Use that image to combine different materials: