/// <summary>
 /// Called when a renderer is unassigned from this planet renderer
 /// </summary>
 private void UnlinkRenderer( IPlanetEnvironmentRenderer renderer )
 {
     if ( renderer != null )
     {
         m_Renderers.Remove( renderer );
     }
 }
 /// <summary>
 /// Called when a renderer is assigned to this planet renderer
 /// </summary>
 private void LinkRenderer( IPlanetEnvironmentRenderer renderer )
 {
     if ( renderer != null )
     {
         renderer.PlanetRenderer = this;
         m_Renderers.Add( renderer );
     }
 }