public void RemoveObject(OutlinerObject obj)
{
objects.Remove(obj.Handle);
removeHandleFromListInDict(obj.Handle, objects_by_parentHandle, obj.ParentHandle);
removeHandleFromListInDict(obj.Handle, objects_by_layerHandle, obj.LayerHandle);
removeHandleFromListInDict(obj.Handle, objects_by_materialHandle, obj.MaterialHandle);
}