public float ComputeCameraSpaceRadiusAt(float z)
    {
        ProjectedBoundingBox pbb = ComputeCameraSpaceBoundsAt(z);
        float radius             = 0.5f * Mathf.Max(pbb.size.x, pbb.size.y);

        return(radius);
    }
    public Vector3 ComputeCameraSpaceCentroidAt(float z)
    {
        ProjectedBoundingBox pbb = ComputeCameraSpaceBoundsAt(z);

        return(pbb.center);
    }