You have to find the sketch Line of the path first. This example works with ModelLines:
ModelLine sweepPath = null;
List<ElementId> deleted = null;
using (Transaction t = new Transaction(doc,"deleteTemp"))
{
t.Start();
deleted = doc.Delete(sweep.Id).ToList();
t.RollBack();
}
List<ModelLine> pathCurveLoop = new List<ModelLine>();
bool firstModellineSection = false;
foreach( ElementId id in deleted)
{
ModelLine ml = doc.GetElement(id) as ModelLine;
if ( ml==null && firstModellineSection) break;
if (ml == null ) continue;
pathCurveLoop.Add(ml);
firstModellineSection = true;
}
sweepPath = pathCurveLoop.FirstOrDefault();
then you can lock the alignment to the referencePlane:
bool alignFirstPoint ;
Reference endPointRef = alignFirstPoint? sweepPath.GeometryCurve.GetEndPointReference(0): sweepPath.GeometryCurve.GetEndPointReference(1);
doc.FamilyCreate.NewAlignment(doc.ActiveView, refPlane.GetReference(),endPointRef);
the method doc.FamilyCreate.NewAlignment won't work if the endpoint of the referenceLine doesn't lie on the referencePlane.
