AddFreeSCS Method can't handle 0 spiral length

[soonhui]

I really wish AddFreeSCS can handle 0 spiral length. Alas it can't.

Because AddFreeSCS with 0 spiral length at both ends, is just AddFreeCurve. And things are easy if it's 0 spiral length at both ends. I can just check whether this is the condition and switch to using AddFreeCurve.

But what if it's only 0 spiral length at one end? How can I handle this case properly? I can't get the API to work , any ideas? 

Here's how to reproduce it. Open the attached drawing in Civil 3D, and then run the following code:

       public static Point3d ToPoint3d(this Point2d pt)
       {
           return new Point3d(pt.X, pt.Y, 0);
       }
   

 private static void Transact(Action<Transaction> action)
    {
        var doc = Application.DocumentManager.MdiActiveDocument;
        using var tr = doc.TransactionManager.StartTransaction();
        action(tr);
        tr.Commit();
    }  


       public static T SingleEntity<T>(this IEnumerable<ObjectId> objectIds,
           Transaction ts, OpenMode openMode)
           where T : DBObject
       {
           var allEntities = new List<T>();
           foreach (ObjectId objectId in objectIds)
           {
               var theObj = ts.GetObject<T>(objectId, openMode);
               if (theObj != null)
                   allEntities.Add(theObj);

           }

           if (allEntities.Count != 1)
               throw new ArgumentException();
           return allEntities.Single();
       }

       
       public static T SingleEntity<T>(this ObjectIdCollection objectIds,
           Transaction ts, OpenMode openMode = OpenMode.ForRead)
           where T : DBObject
       {
           return SingleEntity<T>(objectIds.Cast<ObjectId>(), ts, openMode);
       }

        public static T GetObject<T>(this Transaction ts, ObjectId objectId, OpenMode openMode = OpenMode.ForRead)
        where T:DBObject
        {
            return ts.GetObject(objectId, openMode) as T;
        }


    [CommandMethod(nameof(WriteAlignment1))]
      public void WriteAlignment1()
      {
          Transact(tr =>
          {
              var singleAlignment = ActiveCivil3DDocument.GetAlignmentIds()
                  .SingleEntity<Alignment>(tr);


              var allLines = singleAlignment.Entities.OfType<AlignmentLine>().ToList();
              var firstLine = allLines[0];
              Debug.Assert(firstLine.EntityType == AlignmentEntityType.Line);
              var firstPoint = firstLine.StartPoint;
              var secondPoint = firstLine.EndPoint;


              var spiralIn = (AlignmentSpiral)singleAlignment.Entities[1];
              Debug.Assert(spiralIn.EntityType == AlignmentEntityType.Spiral);

              var curve = (AlignmentArc)singleAlignment.Entities[2];
              var spiralOut = (AlignmentSpiral)singleAlignment.Entities[3];


              var secondLine = allLines[1];
              Debug.Assert(secondLine.EntityType == AlignmentEntityType.Line);


              var firstLabelSetStyles = ActiveCivil3DDocument.Styles.LabelSetStyles.AlignmentLabelSetStyles[0];

              var copyAlignmentId = Alignment.Create(ActiveCivil3DDocument, "copycat", ObjectId.Null,
                  singleAlignment.LayerId, singleAlignment.StyleId, firstLabelSetStyles
                  , AlignmentType.Centerline);
              ActiveCivil3DDocument.GetAlignmentIds().Add(copyAlignmentId);
              var copyAlignment = tr.GetObject<Alignment>(copyAlignmentId);
              var copycatLine1 = copyAlignment.Entities.AddFixedLine(firstPoint.ToPoint3d(),
                  secondPoint.ToPoint3d());
              Debug.Assert(copycatLine1.StartPoint == firstPoint);
              Debug.Assert(copycatLine1.EndPoint == secondPoint);

              var copycatLine2 = copyAlignment.Entities.AddFixedLine
                  (secondLine.StartPoint.ToPoint3d(), secondLine.EndPoint.ToPoint3d());

              var spiralInCopy = copyAlignment.Entities.AddFloatSpiral(copycatLine1.EntityId,
                  curve.Radius, spiralIn.Length, true, SpiralType.Clothoid);
              var spiralOutCopy = copyAlignment.Entities.AddFloatSpiral(curve.Radius, spiralOut.Length,
                  copycatLine2.EntityId, false, SpiralType.Clothoid);
              var curveCopy = copyAlignment.Entities.AddFreeCurve(spiralInCopy.EntityId, spiralOutCopy.EntityId,
                  curve.Radius, CurveParamType.Radius, false, CurveType.Compound);  //crash here
               //the below works
              //var copycatSCS = copyAlignment.Entities.AddFreeSCS(copycatLine1.EntityId, copycatLine2.EntityId,
              //    spiralIn.Length, spiralOut.Length, SpiralParamType.Length,
              //    curve.Radius, false, SpiralType.Clothoid);  //the angle is the angle of the arc
          });
      }

If it really works, then an incomplete alignment mimicking the original alignment will be created, with a few curves and lines at the front exactly the same. 

But in my code above, it crashes at AddFreeCurve due to Invalid Argument or something. 

[hippe013]

Check out this thread.

How To Set the Length property of AlignmentSubEntitySpiral to 0 - Autodesk Community

[soonhui]

@hippe013 ,

I'm not entirely clear on that thread, how your code is supposed to help in setting the Spiral length=0. All I see is that you are transforming an AlignmentSCS to Spiral, Curve and Spiral; 3 AlignmentCurves. 

Can you be more explicit about it?

The thing is that, I need it to be AlignmentSCS because I would need to use the AddAutoWidenings method, which explicitly expect AlignmentSubEntityArc, so AlignmentArc simply won't do at all.