生成截面几何问题

[CommandMethod("CreateView", CommandFlags.UsePickSet | CommandFlags.Redraw | CommandFlags.Modal)]
public void CreateView()
{
        Document doc = Application.DocumentManager.MdiActiveDocument;
        Database db = doc.Database;
        Editor ed = doc.Editor;
        Point3dCollection pts = new Point3dCollection();
        // Get Corner 1
        PromptPointResult ppr1 = ed.GetPoint("\nPick Top Left Corner: ");
        if (ppr1.Status != PromptStatus.OK)
                return;
        // Get Corner 2
        PromptCornerOptions pco2 = new PromptCornerOptions("\nPick Bottom Right Corner: ", ppr1.Value);
        PromptPointResult ppr2 = ed.GetCorner(pco2);
        if (ppr2.Status != PromptStatus.OK)
                return;
        // Get Left, Right and Middle Points
        double wHeight = ppr1.Value.Y - ppr2.Value.Y;
        double midPoint = ppr2.Value.Y + (wHeight / 2);
        Point3d lPt = new Point3d(ppr1.Value.X, midPoint, 80000);
        Point3d rPt = new Point3d(ppr2.Value.X, midPoint, 80000);
        pts.Add(lPt);
        pts.Add(rPt);
        // Start Transaction
        using (Transaction tr = db.TransactionManager.StartTransaction())
        {
                try
                {
                        BlockTable bt = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead);
                        BlockTableRecord ms = (BlockTableRecord)tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite);
                        // Create Section
                        Section sec = new Section(pts, Vector3d.YAxis);
                        sec.State = SectionState.Plane;
                        // Add section to the drawing
                        ObjectId secId = ms.AppendEntity(sec);
                        tr.AddNewlyCreatedDBObject(sec, true);
                        // Set up some of its direct properties and settings
                        sec.SetHeight(SectionHeight.HeightAboveSectionLine, wHeight / 2);
                        sec.SetHeight(SectionHeight.HeightBelowSectionLine, wHeight / 2);
                        SectionSettings ss = (SectionSettings)tr.GetObject(sec.Settings, OpenMode.ForWrite);
                        ss.CurrentSectionType = SectionType.Section2d;
                        ss.SetGenerationOptions(SectionType.Section2d, SectionGeneration.SourceAllObjects | SectionGeneration.DestinationNewBlock);
                        
                        ss.SetVisibility(SectionType.Section2d, SectionGeometry.IntersectionFill, false);
                        ss.SetVisibility(SectionType.Section2d, SectionGeometry.IntersectionFill, false);
                        ss.SetVisibility(SectionType.Section2d, SectionGeometry.CurveTangencyLines, false);
                        ss.SetVisibility(SectionType.Section2d, SectionGeometry.BackgroundGeometry, true);
                        ss.SetHiddenLine(SectionType.Section2d, SectionGeometry.BackgroundGeometry, false);
                        Autodesk.AutoCAD.Colors.Color c = new Autodesk.AutoCAD.Colors.Color();
                        c = Autodesk.AutoCAD.Colors.Color.FromColorIndex(Autodesk.AutoCAD.Colors.ColorMethod.ByLayer, 256);
                        ss.SetColor(SectionType.Section2d, SectionGeometry.BackgroundGeometry, c);
                        ss.SetLayer(SectionType.Section2d, SectionGeometry.BackgroundGeometry, "*_2D");
                        ss.SetLinetype(SectionType.Section2d, SectionGeometry.BackgroundGeometry, "ByLayer");
                        ss.SetLineWeight(SectionType.Section2d, SectionGeometry.BackgroundGeometry, LineWeight.ByLayer);
                        
                        tr.Commit();
                        ed.WriteMessage("\n" + "Section created successfully");
                }
                catch (System.Exception ex)
                {
                        ed.WriteMessage("\nException: " + ex.Message);
                }
        }
}