init method
Implementation
void init(Coordinate p0, Coordinate p1) {
this.p0 = p0;
this.p1 = p1;
dx = p1.x - p0.x;
dy = p1.y - p0.y;
quadrant = Quadrant.quadrant(dx, dy);
// TODO Assert.isTrue(! (dx == 0 && dy == 0), "EdgeEnd with identical endpoints found");
}