private void setSphere(Vector3f O, Vector3f A) {
        radius = FastMath.sqrt(((A.x - O.x) * (A.x - O.x) + (A.y - O.y)
                * (A.y - O.y) + (A.z - O.z) * (A.z - O.z)) / 4f) + RADIUS_EPSILON - 1f;
        center.interpolateLocal(O, A, .5f);
    }
Calculates the minimum bounding sphere of 2 points. Used in welzl's
algorithm.

@param O
           The 1st point inside the sphere.
@param A
           The 2nd point inside the sphere.
@see #calcWelzl(java.nio.FloatBuffer)
jme3-core/src/main/java/com/jme3/bounding/BoundingSphere.java