I'm new to using displacement mapping. I've created some objects then mapped them in UV Mapper, going through the procedure to split vertices and assign different material groups to adjacent surfaces to keep Firefly from rounding off the edges. Now everything works fine until I try to use a displacement map on the object. When I render, I end up with the different material groups separating at their edges so you can actually see inside of the object. Am I missing something here? Is there a fall-off setting or something that should be used with displacement to avoid having the edges displaced away from each other? Gromit

In your render settings, next to the checkbox for displacement, there is a little box for numbers. The numbers here must be higher than the number you use for the displacement setting in the material. The setting there may need to be very high, if you are dealing with split vertices, and the displacement will not carry evenly through because of those split vertices (at least, I'm pretty sure abot that last bit, double check with stewer or other smart folks)

I also feather displacement maps so they fade to black at the edges of each material so the edges don't stick out.

Put a Math node between the texture and the displacement channel that subtracts ~0.5. In contrast to bump maps, the neutral value for displacement is 0 (= black).