public bool ArePreviousObservationsVisible {get;}

//The layer must be track aware and spatial for these settings
//to have an effect
if (streamLayer.TrackType != TrackType.Spatial)
  return;
//Must be on QueuedTask
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)
  return;

//Must be on QueuedTask

//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);