public static void print_compare(string prefix, Frame3f v1, g3.Frame3f v2)
{
double dErr =
(v1.Origin - v2.Origin).Length +
((g3.Quaternionf)v1.Rotation - (v2.Rotation)).Length;
DebugUtil.Log(2, "{0} {1} {2} err {3}", prefix, v1.ToString("F8"), v2.ToString(), dErr);
}