@Override
    public void write(JmeExporter e) throws IOException {
        OutputCapsule capsule = e.getCapsule(this);
        capsule.write(center, "center", Vector3f.ZERO);
        capsule.write(up, "up", Vector3f.UNIT_Z);
        capsule.write(innerRadius, "innerRadius", 0f);
        capsule.write(outerRadius, "outerRadius", 1f);
    }
Serialize this ring to the specified exporter, for example when
saving to a J3O file.

@param e (not null)
@throws IOException from the exporter
jme3-core/src/main/java/com/jme3/math/Ring.java