public bool ArePreviousObservationsVisible {get;}

{
  //The layer must be track aware and spatial for these settings
  //to have an effect
  if (streamLayer.TrackType != TrackType.Spatial)
  {
    // not track aware and spatial
  }
  // Note: call within QueuedTask.Run()
  {
    if (!streamLayer.AreTrackLinesVisible)
      streamLayer.SetTrackLinesVisibility(true);
    if (!streamLayer.ArePreviousObservationsVisible)
      streamLayer.SetPreviousObservationsVisibility(true);
  }
}

{
  //The layer must be track aware and spatial for these settings
  //to have an effect

  if (streamLayer.TrackType != TrackType.Spatial)
  {
    // not track aware and spatial
  }

  // Note: call within QueuedTask.Run()
  {
    //Note: Setting PreviousObservationsCount larger than the 
    //"SetExpirationMaxCount()" has no effect
    streamLayer.SetPreviousObservationsCount(6);
    if (!streamLayer.AreTrackLinesVisible)
      streamLayer.SetTrackLinesVisibility(true);
    if (!streamLayer.ArePreviousObservationsVisible)
      streamLayer.SetPreviousObservationsVisibility(true);
  }
}