static PrecisePolygon regularPolygon(DoublePt etc center, double radius, int sides, double rotation) {
  double angle = twoPi()/sides;
  rotation = degToRadian(rotation);
  ret new PrecisePolygon(countIteratorToList(sides, i ->
    addDoublePts(center, scaleDoublePt(radius, doublePt(sin(rotation+angle*i), cos(rotation+angle*i))))));
}