You can apply and adjust the geometric approximation of an object’s various surface types. Your choices are as follows:
• Hardware Display—Does not affect the geometry of NURBS surfaces and curve objects and is used for viewport display purposes only.
• Surface—Affects the entire geometry of NURBS surfaces and curve objects. Surface approximation is often used in conjunction with displacement approximation.
• Surface Trim—Defines how the trimmed edges of NURBS surfaces and surface curve elements are approximated. For example, the rim of a hole cut into a sphere.
The surface, surface trim, and the hardware display options are discussed in Geometry Approximation on NURBS [Surface and Curve Modeling].
• Polygon Mesh—Defines how a polygon object’s surface is approximated. You can specify the discontinuity angle or use the (default) automatic-discontinuity option.
The polygon mesh options are discussed in Geometry Approximation on Polygon Meshes and Subdivision Surfaces [Polygon Modeling].
• Displacement—Approximates areas that have had a displacement assigned to them through a texture. Displacement approximation is directly influenced by the surface–approximation values (for both NURBS meshes and polygons). See the Displacement options [Properties Reference].
For moving objects with displacement, you can optimize the displacement approximation depending on how fast the object is moving by setting the Motion-Based Displacement Quality option on the Optimization tab of the mental ray Render Options Property Editor [Properties Reference]. The automatic reduction of displacement detail on moving objects has a significant impact on rendering performance and memory consumption by cutting down on the typically huge amount of tessellation data that gets generated.
The displaced geometry should have a geometry approximation property applied to it and motion blur must be enabled for the render region and/or the render pass. See Defining and Rendering Motion Blur [Lights and Cameras].
• Hair—Controls geometry approximation for rendering hair. These options are discussed in Setting the Geometry Approximation [Hair].
For Surface, Surface Trim, and Displacement approximation, you are given the choice of Parametric approximation, Length, Distance, Angle (L/D/A) approximation, or Fine approximation technique.
Parametric techniques operate in UV space, while the three length, distance, and angle dependent techniques operate in 3D space, as does the fine technique.
Autodesk Softimage v.7.5