some more experiments...
taking the feed for the displacement from before the Compute Terrain is a bit limiting, so the next step was to test if I could export the displacement further down the chain - after say, you've make some smaller displacements along with surface shading.
Vector displacement seems to work ok, but scalar (non vector displacements) not so well.
Problem is, if I take the displacement after the compute terrain node, looks like diffuse shading gets into the map, when it should be a pure greyscale map:
Scalar displacement with Compute Terrain OFF:
[attachimg=1]
Scalar displacement with Compute Terrain ON
[attachimg=2]
These are using the blue Displacement to Scalar node - I don't seem to have that problem with the Displacement to Vector node
To get around that I used a Displacement to Vector node and converted that into a scalar using this combination of blue nodes:
[attachimg=3]
Is there a better way of converting the vectors to a scalar in this instance? The displacement doesn't match as well as when I plugged it in before the Compute Terrain.
At the end of the day, using outputting vector displacement is the most accurate way to go, but there are situations where regular scalar displacement is the only option (using it with Zbrush fro example) - but it would be great to get the process working as well with scalar displacements as with vector.
p.s attached updated TGD scene files:
