I'd like to be able to merge one terrain model onto another, but I want it to selectively include only points that are lower than existing terrain model. One thought was to use "Create Cut & Fill Volumes", but if I create a terrain model from that, it uses both top-surface and bottom-surface vertices. If I drop complex on that element, it seems that bad things happen and I can't get rid of visual artifacts from it, even if I close and re-open the file. (And this observation irks me.)
Is this a possibility?