public double ClusteringDistance {get; set;}

{
  // must be on MCT 

  var planeFilter = new LasPointPlaneSelectionFilter();
  planeFilter.VisiblePoints = true;
  planeFilter.ClassCodes = new List<int>();  // empty list means all classification codes
  planeFilter.FilterGeometry = polygon;

  planeFilter.ClusteringDistance = 0.3; // meters
  planeFilter.MaximumDistance = 500;
  planeFilter.PlaneTolerance = 0.152; // meters

  var planeSelCount = await lasDatasetLayer.SelectAsync(planeFilter, SelectionCombinationMethod.New);
}