bool Sphere::IsValid(void) const throw() {
    bool   ret                        = false;
    const  rt_ell_internal* internalp = Internal();
    double dist                       = 0.0005 * 0.0005;

    if (!VNEAR_ZERO(internalp->a, SMALL_FASTF) &&
        !VNEAR_ZERO(internalp->b, SMALL_FASTF) &&
        !VNEAR_ZERO(internalp->c, SMALL_FASTF) &&
        NEAR_ZERO(VDOT(internalp->b, Internal()->a ), RT_DOT_TOL)   &&
        NEAR_ZERO(VDOT(internalp->c, Internal()->a ), RT_DOT_TOL)   &&
        NEAR_ZERO(VDOT(internalp->b, Internal()->c ), RT_DOT_TOL)   &&
        NEAR_EQUAL(MAGNITUDE(internalp->a),MAGNITUDE(internalp->b), dist) &&
        NEAR_EQUAL(MAGNITUDE(internalp->b),MAGNITUDE(internalp->c), dist))
        ret = true;

    return ret;
}