3D vector displacement is interesting stuff and now that you mention it, I do not know how the orientation is decided if the prop has no UV map. Note that a normal vector is unambiguous - there is only one normal, or "out" direction no matter what. But perpendicular to that, in tangent space, is an "up" vector that has an infinite number of solutions. I know that normal maps generally rely on the fact that they are UV maps, and they pick the "up" vector that lies in the same plane as the local "V" coordinate seems to point to. In the absence of a UV mapping, I guess there is no unambiguous "up" vector.

In any case, I know the math of 3D displacement and tangent space pretty well and it's much simpler than determining curvature. But thanks for the suggestion.

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