public void Add(I3DLayerRender render)
 {
     if (!list.Contains(render))
     {
         list.Add(render);
     }
 }
        public I3DLayerRender Select(string rendername)
        {
            I3DLayerRender result = null;

            foreach (var provider in Renders)
            {
                if (provider.Name == rendername)
                {
                    result = provider;
                    break;
                }
            }
            return(result);
        }