多段线和二维多段线的区别及顶点遍历

近日项目处理中，在遍历多义线的时候，发现客户的图纸有【二维多段线】这个类型，需要做兼容处理，因此总结记录一下。

在 AutoCAD 里，LWPOLYLINE（轻量级多段线，命令是PL，下图左）和POLYLINE（多段线，本次主要讲述二维多段线，下图右）都是用来表示由多个线段或圆弧连接而成的图形对象，通过属性可以简单查看两者的内容：

1. 数据结构与存储

• LWPOLYLINE：
  • 它属于轻量级对象，存储数据时更为紧凑。相较于POLYLINE，LWPOLYLINE占用的内存和磁盘空间更少，这使得在处理大量多段线对象时，能有效提升性能。
  • 其顶点信息以连续的坐标对形式存储，数据结构较为简单，这也进一步减少了存储空间。
• POLYLINE：
  • 这是一种传统的多段线对象，数据结构相对复杂。它不仅包含顶点信息，还包含更多的属性和扩展数据，因此占用的存储空间更多。

2. 图形特性

• LWPOLYLINE：
  • 只能是二维对象，仅存在于当前 UCS（用户坐标系）的 XY 平面上。
  • 各顶点间的连接方式只能是直线段或圆弧，不能包含其他复杂的曲线。
• POLYLINE：
  • 既可以是二维对象，也可以是三维对象，能在三维空间中表示多段线。
  • 除了直线段和圆弧，还可以包含其他类型的曲线，如样条曲线等，具有更强的图形表达能力。

通过插件，查看两者的组码，内容如下：

从上面的两个图可见，两者组码"0"，即它们的类型是不一样的。组码"0"也是从图纸筛选过滤的类型条件。

笔者通过策略模式，封装了两种模式的顶点遍历方案，核心代码如下：

// 顶点处理策略接口public interface IVertexProcessingStrategy{void ProcessVertices(Entity entity, List<CPointInfo> list);}// 顶点处理策略基类public abstract class VertexProcessingStrategyBase : IVertexProcessingStrategy{public abstract void ProcessVertices(Entity entity, List<CPointInfo> list);public CPointInfo ProcessVertex(Point3d vertex3d){System.Globalization.CultureInfo cultures = new System.Globalization.CultureInfo("en-US");Point3d ptLocation = CommonDeal.TransToLayout_3d(m_vp, vertex3d);return (new CPointInfo(){Num = (listRailCar_RedPointInfo.Count + 1).ToString(),XPos = vertex3d.X.ToString("f1", cultures),YPos = vertex3d.Y.ToString("f1", cultures),location = MathKit.Trans2XYZPoint(vertex3d)});}}// LWPOLYLINE 顶点处理策略public class LwPolylineVertexProcessingStrategy : VertexProcessingStrategyBase{public override void ProcessVertices(Entity entity, List<CPointInfo> list){var lwPoly = entity as Autodesk.AutoCAD.DatabaseServices.Polyline;if (lwPoly != null){int iNumberOfVertices = lwPoly.NumberOfVertices;for (int j = 0; j < iNumberOfVertices; j++){Point2d pt2d = lwPoly.GetPoint2dAt(j);CPointInfo processedPoint = ProcessVertex(new Point3d(pt2d.X, pt2d.Y, 0.0));list.Add(processedPoint);}}}}// POLYLINE 顶点处理策略public class PolylineVertexProcessingStrategy : VertexProcessingStrategyBase{public override void ProcessVertices(Entity entity, List<CPointInfo> list){var poly = entity as Autodesk.AutoCAD.DatabaseServices.Polyline2d;if (poly != null){Point3dCollection aaa = new Point3dCollection();poly.GetStretchPoints(aaa);int nn = aaa.Count;for (int i = 0; i < nn; i++){CPointInfo processedPoint = ProcessVertex(aaa[i]);list.Add(processedPoint);}}}}// 顶点处理上下文public class VertexProcessingContext{private IVertexProcessingStrategy _strategy;public VertexProcessingContext(IVertexProcessingStrategy strategy){_strategy = strategy;}public void SetStrategy(IVertexProcessingStrategy strategy){_strategy = strategy;}public void Process(Entity entity, List<CPointInfo> list){_strategy.ProcessVertices(entity, list);}}public void DealTwoTypePolyline(string sPLineLayer, string sLayoutName = ""){Editor ed = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Editor;// 定义筛选条件TypedValue[] values = new TypedValue[]{// 图元类型为LWPOLYLINE或POLYLINEnew TypedValue((int)DxfCode.Start, "LWPOLYLINE,POLYLINE"),// 图层为sPLineLayernew TypedValue((int)DxfCode.LayerName, sPLineLayer),// 布局名称为sLayoutNamenew TypedValue((int)DxfCode.LayoutName, sLayoutName)};SelectionFilter filter = new SelectionFilter(values);PromptSelectionResult psr;{psr = ed.SelectAll(filter);}if (psr.Status != PromptStatus.OK){return ;}Document document = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;Database db = document.Database;List<CPointInfo> listCPointInfo = new List<CPointInfo>();using (Transaction tr = db.TransactionManager.StartTransaction()){BlockTable bt = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead);BlockTableRecord btr = (BlockTableRecord)tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForRead);var lwPolyStrategy = new LwPolylineVertexProcessingStrategy();var polyStrategy = new PolylineVertexProcessingStrategy();var context = new VertexProcessingContext(lwPolyStrategy);ObjectId[] ids = psr.Value.GetObjectIds();for (int i = 0; i < ids.Length; i++){Entity ent = (Entity)tr.GetObject(ids[i], OpenMode.ForRead);if (ent is Autodesk.AutoCAD.DatabaseServices.Polyline){context.SetStrategy(lwPolyStrategy);}else if (ent is Autodesk.AutoCAD.DatabaseServices.Polyline2d){context.SetStrategy(polyStrategy);}else{continue;}context.Process(ent, listCPointInfo);}tr.Commit();}}