private static S2Point PerturbAtDistance(S1Angle distance, S2Point a0, S2Point b0)
{
S2Point x = S2.InterpolateAtDistance(distance, a0, b0);
if (S2Testing.Random.OneIn(2))
{
for (int i = 0; i < 3; ++i)
{
x = x.SetAxis(i, MathUtils.NextAfter(x[i], S2Testing.Random.OneIn(2) ? 1 : -1));
}
x = x.Normalize();
}
return(x);
}