Feature-based displacement map attributes

• Connect a displacement map.
• Adjust displacement sampling rates.

You can find these attributes under the Displacement Map section of the shape node’s Attribute Editor.

Feature Displacement

Turn on (default) Feature-based Displacement.

Note: We do not recommend that you turn off Feature-based displacement to use non-feature-based displacement.

Initial Sample Rate

This rate is used to check the texture values to determine the difference between displacement heights and where to introduce new vertices. It defines a regular sampling grid in each original tessellation triangle. For example, with the default value of 6, the sample grid is 6x6.

Try to keep this sample rate to a reasonable value since it does take longer to render the higher the value.

For each tessellation triangle, notice how much texture height variation is in the triangle and estimate how many initial samples are required to include these features when displacement mapping. Consider the following:

• If the original triangle is large and the feature in the triangle is fine, then the Initial Sample Rate has to be large to include the fine features.
• If the original triangle is small and the features are sparse, the Initial Sample Rate does not have to be very large. The default of 6 may be enough.

  Extra Sample Rate

  This rate is used to take extra samples to refine the new vertices introduced during displacement mapping. Maya adjusts the vertices to align with the displacement.

  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

  Always try to set this value at 0 first if the result looks too jagged, then increase the value to get the results you need. The default value is 5. A value of 20 is usually enough.

  In the following examples, the displaced surface on the left only needs an Extra Sample Rate value of 0, but the surface on the right needs an Extra Sample Rate of 5.

  

  Texture Threshold

  This value is used to eliminate vertices that do not significantly contribute to the displacement. This is a threshold of the percentage of the maximum height variation. Any vertex where the variation is smaller than this value is not considered. The default value is 0.

  Note: It is recommended that you pre-process the texture so that it contains as little noise as possible and leave this value at the default of 0. Consider the following:

  • If render times are high, you can increase default value slightly.
  • If you have black and white (embossing), the default setting of 0 is optimal.
  • If you have smooth displacement, like a bulge, specify small values (as close to 0 as possible).

  Normal Threshold

  Determine the angle threshold of the normal difference between two adjacent triangles (the angular value is in degrees). If the normal difference is higher than the threshold, the edge between these two triangles is recognized as a sharp edge. If lower, the normals are averaged which produces smooth edges. The default value is 30 degrees.

  Note: It is recommended that you leave this value at the default of 30.

  Bounding Box Scale

  Determines the bounding box scale for a displacement map and helps to compute the bounding box scale automatically by tessellating the object.

  Bounding Box Scale lets you estimate the size of a displaced object’s bounding box. It is in world space because the displacement is applied to vertices in world space. Based on the bounding box scale, Maya calculates the new bounding box for the displacement-mapped object.

  When you scale the bounding box, make sure it is not too small or the displacement may look cut-off or look as though it has holes. The default bounding box scale (1.5 in world space) should be adequate in most situations; however, if you want large-scale displacement, increase the bounding box scale significantly. If you do not increase the size enough, artifacts result in the rendered image, but if the estimate is too large, Maya may use more memory to render the object.

  Attention: Be careful if you have an animation that changes the relationship between the displacement and the size of the surface being displaced. Choose the most extremely-displaced frame to perform the Calculate Bounding Box Scale operation. Alternatively, animate the value manually.