Iray Programmer's Manual

Tessellating curved surfaces

To appear smooth when rendered, smooth curved surfaces must be tessellated with enough detail. Especially in areas of high curvature shading artifacts may occur if the geometry is not sufficiently tessellated. Shadow edges appear to be blocky; faces are shaded when they shouldn't be. This phenomenon is called shadow terminator artifact. If the silhouette looks under-tessellated, it is likely that shadow terminator problems will occur as well. Increase the tessellation of the geometry to avoid shadow terminator artifacts.

Figure 1. Poorly tessellated geometry showing bad shadow artifacts at the edge of the nose.
File: images/nose_tessellation_coarse.jpg
Figure 2. Same object with finer tessellation.
File: images/nose_tessellation_fine.jpg
Figure 3. Poorly tessellated objects do not look good in general.
File: images/knot_tessellation_coarse.jpg
Figure 4. Same object with proper tessellation.
File: images/knot_tessellation_fine.jpg