RESOLVED: Basically, pilot error. Somehow I had 'Apply displacement' enabled for the Image Map Shader with an amplitude of 1.35. It's a mystery to me, but that was the problem. Unchecking the Apply Displacement brought everything together...though I'm still curious why I could not manage to get the grass to sit on the terrain even when linked to the Image Map node.
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I'm working on a scene that has sand covered terrain, with rocks scattered about. Basically the node tree is: compute terrain->Base Colours->(an Image Map)->(sand and rocks merged)->Planet 01
When I bring in a grass population, it hooks to the output of the "Compute Terrain" node, which I suppose is the default. The problem is the grass is beneath the sand/rock/image map terrain...if I tilt the camera to view beneath the surface, there's the grass, about a meter underneath. I've tried setting the grass node to 'sit' on the Image Map node, the Sand node, and Base Colours, as well as the Compute Terrain--but it never moves, just stays underneath.
Can someone suggest what I may be missing? I've looked, but can't spot anything glaringly obvious.
Thanks.
