E8 - Petrie Projection

The 240 roots of E8, built as the 112 vectors +/-e_i +/-e_j and the 128 vectors (+/-1/2)^8 with an even number of minus signs, then projected onto the Coxeter plane. That plane is the eigenplane of the Coxeter element for eigenvalue exp(2 pi i / 30), which sorts the roots into eight rings of thirty. Every pair of roots at inner product 1 is joined, giving 6720 edges. Edge colour follows the mean projected radius.