To determine how to set the Initial and Extra sample rates

1. Make sure the displacement mapped object is selected and its Attribute Editor appears.
2. Display the tessellation triangles of the object.
3. Preview the displacement results.
4. For each tessellation triangle, look at how much texture height variation is in the triangle, then (in the Displacement Map section of the object’s Attribute Editor), adjust the Initial Sample Rate.
5. For each tessellation triangle, notice how sharp the features are and how many curvy features there are. The sharper the features, the higher the Extra Sample Rate needs to be; adjust accordingly.