A triangle fan is a series of connected triangle faces. The first three vertices (denoted below by v1, v2, and v3), define the first triangular face. A new triangle is formed by connecting the next point with its immediate predecessor and the first point of the triangle fan. That is, every additional point vi defines a new triangular face with vertices v1, vi-1, and vi.
For example, the second triangle is defined by v1, v3, v4, the third by v1, v4, v5, and so on. The following diagram illustrates a typical triangle fan.
The orientation of the triangle fan is determined by the order of vertices of any triangle within the fan. For more information on how vertex order affects surface normal and front/back surface determination, see Faces.
Triangle fans may store measures on their nodes.