public bool IsTargetVisibleFromObserverPoint {get;}

{
  tinLayer = null;
  MapPoint observerPoint = null;
  MapPoint targetPoint = null;
  CIMPointSymbol obstructionPointSymbol = null;
  CIMLineSymbol visibleLineSymbol = null;
  CIMLineSymbol invisibleLineSymbol = null;

  var losParams = new LineOfSightParams();
  losParams.ObserverPoint = observerPoint;
  losParams.TargetPoint = targetPoint;

  // add offsets if appropriate
  // losParams.ObserverHeightOffset = observerOffset;
  // losParams.TargetHeightOffset = targerOffset;

  // add obstruction feature class if appropriate (multipatch)
  //losParams.ObstructionsMultipatchFeatureClass = obsFeatureClass;

  // set output spatial reference
  losParams.OutputSpatialReference = MapView.Active.Map.SpatialReference;

  LineOfSightResult results = null;
  try
  {
    // Note: Needs QueuedTask to run
    {
      if (tinLayer.CanGetLineOfSight(losParams))
        results = tinLayer.GetLineOfSight(losParams);
    }
  }
  catch (Exception)
  {
    // handle exception
  }

  if (results != null)
  {
    bool targetIsVisibleFromObserverPoint = results.IsTargetVisibleFromObserverPoint;
    //These properties are not used. They will always be false
    // results.IsTargetVisibleFromVisibleLine;
    // results.IsTargetVisibleFromInvisibleLine;

    if (results.VisibleLine != null)
      MapView.Active.AddOverlay(results.VisibleLine, visibleLineSymbol.MakeSymbolReference());
    if (results.InvisibleLine != null)
      MapView.Active.AddOverlay(results.VisibleLine, invisibleLineSymbol.MakeSymbolReference());
    if (results.ObstructionPoint != null)
      MapView.Active.AddOverlay(results.ObstructionPoint, obstructionPointSymbol.MakeSymbolReference());
  }
}