Smoothing group
Encyclopedia
In 3D computer graphics
, a smoothing group is a group of polygon
s in a polygon mesh
which should appear to form a smooth surface. Smoothing groups are useful for describing shape
s where some polygons are connected smoothly to their neighbors, and some are not. For example, in a mesh representing a cylinder
, all of the polygons are smoothly connected except along the edges of the end caps. One could make a smoothing group containing all of the polygons in one end cap, another containing the polygons in the other end cap, and a last group containing the polygons in the tube shape between the end caps.
By identifying the polygons in a mesh that should appear to be smoothly connected, smoothing groups allow 3D modeling software to estimate the surface normal
at any point on the mesh, by averaging the surface normal
s or vertex normals in the mesh data that describes the mesh. The software can use this data to determine how light interacts with the model. If each polygon lies in a plane, the software could calculate a polygon's surface normal by calculating the normal of the polygon's plane, meaning this data would not have to be stored in the mesh. Thus, early 3D modeling software like 3D Studio Max DOS used smoothing groups as a way to avoid having to store accurate vertex normals for each vertex of the mesh, as a strategy for computer representation of surfaces
.
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
, a smoothing group is a group of polygon
Polygon
In geometry a polygon is a flat shape consisting of straight lines that are joined to form a closed chain orcircuit.A polygon is traditionally a plane figure that is bounded by a closed path, composed of a finite sequence of straight line segments...
s in a polygon mesh
Polygon mesh
A polygon mesh or unstructured grid is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling...
which should appear to form a smooth surface. Smoothing groups are useful for describing shape
Shape
The shape of an object located in some space is a geometrical description of the part of that space occupied by the object, as determined by its external boundary – abstracting from location and orientation in space, size, and other properties such as colour, content, and material...
s where some polygons are connected smoothly to their neighbors, and some are not. For example, in a mesh representing a cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
, all of the polygons are smoothly connected except along the edges of the end caps. One could make a smoothing group containing all of the polygons in one end cap, another containing the polygons in the other end cap, and a last group containing the polygons in the tube shape between the end caps.
By identifying the polygons in a mesh that should appear to be smoothly connected, smoothing groups allow 3D modeling software to estimate the surface normal
Surface normal
A surface normal, or simply normal, to a flat surface is a vector that is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a...
at any point on the mesh, by averaging the surface normal
Surface normal
A surface normal, or simply normal, to a flat surface is a vector that is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a...
s or vertex normals in the mesh data that describes the mesh. The software can use this data to determine how light interacts with the model. If each polygon lies in a plane, the software could calculate a polygon's surface normal by calculating the normal of the polygon's plane, meaning this data would not have to be stored in the mesh. Thus, early 3D modeling software like 3D Studio Max DOS used smoothing groups as a way to avoid having to store accurate vertex normals for each vertex of the mesh, as a strategy for computer representation of surfaces
Computer representation of surfaces
In technical applications of 3D computer graphics such as computer-aided design and computer-aided manufacturing, surfaces are one way of representing objects. The other ways are wireframe and solids...
.