Revit API畫垂直於風管的風管

start
[Transaction(TransactionMode.Manual)]
[Regeneration(RegenerationOption.Manual)]
  cmd : IExternalCommand
{
     Result Execute(ExternalCommandData cmdData,   msg, ElementSet elements)
    {
        UIDocument uiDoc = cmdData.Application.ActiveUIDocument;
        UIApplication uiApp = cmdData.Application;
        Document doc = uiDoc.Document;
        Selection selection = uiDoc.Selection;

        Transaction ts =  Transaction(doc, );
        ts.Start();
                DuctType ductType = ;
        FilteredElementCollector collector =  FilteredElementCollector(doc);
        collector.OfClass((DuctType));
         (Element el  collector.ToElements())
        {
            ductType = el  DuctType;
            ;
        }
                Reference refDuct = selection.PickObject(ObjectType.Element, );
        Duct duct = doc.GetElement(refDuct)  Duct;
        XYZ xyz = selection.PickPoint();        LocationCurve lCurve = duct.Location  LocationCurve;
        IntersectionResult interResult = lCurve.Curve.Project(xyz);         (interResult != )
        {
            doc.Create.NewDuct(xyz, interResult.XYZPoint, ductType);
        }
        ts.Commit();
         Result.Succeeded;
    }
}url:http://greatverve.cnblogs.com/p/Curve-Project.html