public static BoundingBox ExtendBy(this BoundingBox bb, BoundingBox next) {
return new BoundingBox(
new Vector3(
Math.Min(bb.Minimum.X, next.Minimum.X),
Math.Min(bb.Minimum.Y, next.Minimum.Y),
Math.Min(bb.Minimum.Z, next.Minimum.Z)),
new Vector3(
Math.Max(bb.Maximum.X, next.Maximum.X),
Math.Max(bb.Maximum.Y, next.Maximum.Y),
Math.Max(bb.Maximum.Z, next.Maximum.Z)));
}