public void unassociateFromGroupNode() {
        if (groupNode != null) {
            // Once the geometry is removed
            // from the parent, the group node needs to be updated.
            groupNode.onGeometryUnassociated(this);
            groupNode = null;

            // change the default to -1 to make error detection easier
            startIndex = -1;
        }
    }
Removes the {@link GeometryGroupNode} association from this
<code>Geometry</code>.

Should only be called by the parent {@link GeometryGroupNode}.
jme3-core/src/main/java/com/jme3/scene/Geometry.java