3. Node, edge, and face ordering

For a triangle, the node and edge numbering follows a counterclockwise scheme, with the lower left attribute starting at 1 (tie breaking goes to the lower of the two, such (1,0) over (0,1) in a triangle formed by (0,1), (1,0), and (1,1)). After the vertices are numbered 1-3, the nodes between vertices on an edge are numbered. Working up through the edges by number, their node numbers count up from the vertex with lower node number to higher node number.

Interior node ordering is based on the active symmetry orbits and follows no easily described pattern.

The figures below show the node indices on the reference elements for p=1 through p=4