I'm reading the book Computational Geometry in C by O'Rourke. One of the problems ask the following
Diagonals$\rightarrow$triangulation. Given a list of diagonals of a polygon forming a triangulation, with each diagonal specified by a counterclockwise indices of the endpoints, design an algorithm to build the triangulation dual tree.
While I have a vague idea of how to solve the given problem, it isn't clear to me what exactly diagonal specified by a counterclockwise indices of the endpoints mean as this seems important in the algorithm design.
O'Rourke's own sample input (below) specified a list of coordinates which isn't obvious to me how they are a list of diagonals.
0 0 10 7 12 3 20 8 13 17 10 12 12 14 14 9 8 10 6 14 10 15 7 18 0 16 1 13 3 15 5 8 -2 9 5 5
I would be grateful if someone could give a hint on either what the counterclockwise indices of the endpoints mean, or how the list of points above translates to a list of diagonals. Thank you.