vectorForAngleIndex (i: number): OffsetCoords2d {
let v: OffsetCoords2d;
if (i == 0) {
v = this.apex.asOffsetFromOrigin();
} else {
v = OffsetCoords2d.fromDxDy(1 - this.apex.x, -this.apex.y);
}
return v.times(v).timesReal(1.0 / v.squaredLength());
}