ABSTRACT
A triangle T is given by three points, its vertices, p1, p2, and p3. The vertices may live in 2D or 3D. Three points define a plane, thus a triangle is a 2D element. We use the convention of labeling the pi in a counterclockwise sense. The edge, or side, opposite point pi is labeled si. (See Sketch 8.1.)
When we study properties of this triangle, it is more convenient to work in terms of a local coordinate system which is closely tied to the triangle. This type of coordinate system was invented by F. Moebius and is known as barycentric coordinates.
