How to copy a part of polyline

[Anonymous]

Hi,everyone,

I am a beginer of AutoCAD.net. My question is how to create a new polyline which vertex is from a old polyline.
My code seems have a copy a polyline in debug, but I can't find the new polyline in AutoCAD,why?

The code is below:

        [CommandMethod("CopyPartPolyline")]
        public void CopyPartPolyline()
        {
            Document acDoc = Application.DocumentManager.MdiActiveDocument;
            Database acCurDb = acDoc.Database;

            Polyline pline = selectOnePolyline(acCurDb); //prompt user to select a polyline from screen

            using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
            {
                BlockTable acBlkTbl;
                acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId,OpenMode.ForRead) as BlockTable;

                BlockTableRecord acBlkTblRec;
                acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace],OpenMode.ForWrite) as BlockTableRecord;

                // Create a lightweight polyline
                Polyline acPoly = new Polyline();
                acPoly.SetDatabaseDefaults();
                for (int i = 0; i < pline.NumberOfVertices; i=i+2)
                {
                    double x = pline.GetPoint2dAt(i).X; double y = pline.GetPoint2dAt(i).Y;
                    acPoly.AddVertexAt(i/2, new Point2d(x, y), 0, 0, 0);
                }
                acBlkTblRec.AppendEntity(acPoly);
                acTrans.AddNewlyCreatedDBObject(acPoly, true);
                acPoly.Closed = true;
                acTrans.Commit();
            }

[Balaji_Ram]

Hi,

The "index" parameter in the call to "AddVertexAt" seems to be wrong.

You will need to check the code carefully. As a first step, try creating a copy of the original polyline. After that is done, you may modify it the way you want the new polyline to appear.

Here is the first step :

			Document activeDoc = Application.DocumentManager.MdiActiveDocument;
			Database db = activeDoc.Database;
			Editor ed = activeDoc.Editor;

			PromptEntityOptions peo = new PromptEntityOptions("Select a polyline : ");
			peo.SetRejectMessage("Not a polyline");
			peo.AddAllowedClass(typeof(Autodesk.AutoCAD.DatabaseServices.Polyline), true);
			PromptEntityResult per = ed.GetEntity(peo);
			if (per.Status != PromptStatus.OK)
				return;

			using (Transaction acTrans = db.TransactionManager.StartTransaction())
			{
				BlockTable acBlkTbl;
				acBlkTbl = acTrans.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;

				Autodesk.AutoCAD.DatabaseServices.Polyline pline = acTrans.GetObject(per.ObjectId, OpenMode.ForRead) as Autodesk.AutoCAD.DatabaseServices.Polyline;

				BlockTableRecord acBlkTblRec;
				acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;

				// Create a lightweight polyline
				Autodesk.AutoCAD.DatabaseServices.Polyline acPoly = new Autodesk.AutoCAD.DatabaseServices.Polyline();
				acPoly.SetDatabaseDefaults();

				int index = 0;
				for (int i = 0; i < pline.NumberOfVertices; i++)
				{
					double x = pline.GetPoint2dAt(i).X; 
					double y = pline.GetPoint2dAt(i).Y;
					acPoly.AddVertexAt(index, new Point2d(x, y), 0, 0, 0);
					index++;
				}
				acBlkTblRec.AppendEntity(acPoly);
				acTrans.AddNewlyCreatedDBObject(acPoly, true);
				acPoly.Closed = true;
				acTrans.Commit();
			}

[Hallex]

Here is quick and dirty example to copy segment of polyline,

see if this what you looking for

        [CommandMethod("copyseg")]
        public void copySegment()
        {
            Document doc = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
            Editor ed = doc.Editor;
            Database db = doc.Database;
            PromptEntityOptions peo = new PromptEntityOptions("\nSelect the segment to copy: ");
            peo.SetRejectMessage("\nYou have to select polyline only!");
            peo.AllowNone = false;
            peo.AllowObjectOnLockedLayer = false;
            peo.AddAllowedClass(typeof(Polyline), true);
            PromptEntityResult per = ed.GetEntity(peo);
            if (per.Status == PromptStatus.OK)
            {
  
                ObjectId objId = per.ObjectId;
                try
                {
                    using (Transaction tr = db.TransactionManager.StartTransaction())
                    {
                        Polyline pline = tr.GetObject(objId, OpenMode.ForRead, false) as Polyline;
                        if (pline != null)
                        {
                            BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId,OpenMode.ForWrite, false) as BlockTableRecord;
                            Point3d pickPt = pline.GetClosestPointTo((Point3d)per.PickedPoint, false);
                            double param = pline.GetParameterAtPoint(pickPt);
                            int index = (int)param;
                          double swid=  pline.GetStartWidthAt(index);
                          double ewid = pline.GetEndWidthAt(index);

                          SegmentType stype=  pline.GetSegmentType(index);
                          if (stype == SegmentType.Line)
                          {
                             LineSegment2d lineseg= pline.GetLineSegment2dAt(index);
                              Polyline spoly = new Polyline();
                              Point2d sp = lineseg.StartPoint;
                              Point2d ep = lineseg.EndPoint;
                              spoly.AddVertexAt(0, sp, 0, swid, ewid);
                              spoly.AddVertexAt(1, ep,0,swid,ewid);
                              spoly.ColorIndex = 1;
                              btr.AppendEntity(spoly);
                              tr.AddNewlyCreatedDBObject(spoly, true);

                          }
                          if (stype == SegmentType.Arc)
                          {
                              CircularArc2d arcseg = pline.GetArcSegment2dAt(index);
                              Polyline spoly = new Polyline();
                              Point2d sp = arcseg.StartPoint;
                              Point2d ep = arcseg.EndPoint;
                              double boo = pline.GetBulgeAt(index);

                              spoly.AddVertexAt(0, sp, boo, swid, ewid);
                              spoly.AddVertexAt(1, ep, boo, swid, ewid);
                              spoly.ColorIndex = 2;
                              btr.AppendEntity(spoly);
                              tr.AddNewlyCreatedDBObject(spoly, true);

                          }
                        }
                        tr.Commit();
                    }
                }
                catch (System.Exception ex)
                {
   
                    ed.WriteMessage("\nError: {0}\nTrace: {1}" , ex.Message , ex.StackTrace);
                }
            }
        }

~'J'~

[Anonymous]

Thanks for reply of Balaji_Ram and  Hallex. Maybe my poor representation,gives a misunderstand.

In fact,I want to extract a part of vertex from a old polyline to form a new polyline.For example,my code intends to get 0,2,4,6,... vertex from pline,then to create a new polyline named acPoly.
The motive behind my question is to simplify contour lines in terrain which own too dense vertex. Anyone can help me?thanks.

[Balaji_Ram]

In the code snippet that I earlier posted, replace this code and try it.

		int index = 0;
		for (int i = 0; i < pline.NumberOfVertices; i++)
		{
			if (i % 2 == 0)
			{
				double x = pline.GetPoint2dAt(i).X;
				double y = pline.GetPoint2dAt(i).Y;
				acPoly.AddVertexAt(index, new Point2d(x, y), 0, 0, 0);
				index++;
			}
		}

[Anonymous]

That's OK. Thanks,Balaji_Ram.

Another,I know why I can't find new polyline on screen. I used "db.GetObject()",but not "acTrans.GetObject()".