When you render a model, the density of the mesh affects the smoothness of surfaces.
Mesh objects are comprised of the following components:
- Vertex. A point that forms the corner of a face or polygon.
- Face. A triangular portion of a surface object.
- Polygon. A quadrilateral portion of a surface object.
- Edge. The boundary of a face or polygon.
In a drawing, all faces have three vertices, except faces in polyface meshes, which are treated as adjoining triangles. For rendering purposes, each quadrilateral face is a pair of triangular faces that share one edge.
Smoothing of an object is handled automatically by the renderer. Two types of smoothing occur during the rendering process. One smoothing operation interpolates the face normals across a surface. The other operation takes into account the number of faces, or face count, that make up the geometry; greater face counts result in smoother surfaces but longer processing times.
While you cannot control the interpolation of face normals, you can control the display accuracy of curved objects by using the VIEWRES command and FACETRES system variable.
Control Display of Curves
The VIEWRES command controls the display accuracy of curved 2D linework such as circles and arcs in the current viewport.
In the following example, line segments are more apparent as VIEWRES decreases - Upper left = 1000, Middle = 100, Lower right = 10.
These objects are drawn on the screen using many short straight line segments. Smoother arcs and circles result from higher VIEWRES settings, but they take longer to regenerate. To improve performance while you're drawing, set a low VIEWRES value.
Control Display of Curved Solids
FACETRES controls the mesh density and smoothness of shaded and rendered curved solids.
In the following example, facets are displayed on curved geometry when FACETRES is low (FACETRES = .25).
When FACETRES is set to 1, there is a one-to-one correlation between the viewing resolution of circles and arcs and the tessellation, a means of subdividing the faces of solid objects. For example, when FACETRES is set to 2, the tessellation will be twice the tessellation set by VIEWRES. The default value of FACETRES is 0.5. The range of possible values is 0.01 to 10.
When you raise and lower the value of VIEWRES, objects controlled by both VIEWRES and FACETRES are affected. When you raise and lower the value of FACETRES, only solid objects are affected.
In the following example, smoother geometry is displayed when FACETRES is set to a higher value (FACETRES = 5).
