Polyline2d Class

Overview

The Polyline2d class represents a legacy 2D polyline entity in AutoCAD. Unlike the lightweight Polyline class, Polyline2d is a container object that owns a collection of Vertex2d objects. Each vertex is a separate database object. This class is primarily used for compatibility with older drawings and for polylines that require per-vertex extended data.

Namespace

Autodesk.AutoCAD.DatabaseServices

Inheritance Hierarchy

System.Object
  └─ RXObject
      └─ DBObject
          └─ Entity
              └─ Curve
                  └─ Polyline2d

Key Properties

Property	Type	Description
`PolyType`	`Poly2dType`	Gets/sets the polyline type (SimplePoly, FitCurvePoly, QuadSplinePoly, CubicSplinePoly)
`DefaultStartWidth`	`double`	Gets/sets the default starting width for vertices
`DefaultEndWidth`	`double`	Gets/sets the default ending width for vertices
`Thickness`	`double`	Gets/sets the polyline thickness (extrusion)
`Elevation`	`double`	Gets/sets the elevation (Z coordinate)
`Normal`	`Vector3d`	Gets/sets the normal vector
`Closed`	`bool`	Gets/sets whether the polyline is closed
`LinetypeGenerationOn`	`bool`	Gets/sets whether linetype generation is continuous
`Length`	`double`	Gets the total length of the polyline

Key Methods

Method	Return Type	Description
`GetEnumerator()`	`IEnumerator`	Gets an enumerator for vertices
`AppendVertex(Vertex2d)`	`void`	Appends a vertex to the polyline
`InsertVertexAt(int, Vertex2d)`	`void`	Inserts a vertex at the specified index
`OpenVertex(Vertex2d, OpenMode)`	`Vertex2d`	Opens a vertex for read or write
`ConvertToPolylineType(Poly2dType)`	`void`	Converts the polyline to a different type
`Straighten()`	`void`	Removes all curve fitting
`SplineFit()`	`void`	Applies spline fitting

Code Examples

Example 1: Creating a Polyline2d

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTable bt = tr.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
    BlockTableRecord btr = tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;
    
    // Create the polyline container
    Polyline2d poly = new Polyline2d();
    poly.SetDatabaseDefaults();
    
    // Add polyline to the drawing
    ObjectId polyId = btr.AppendEntity(poly);
    tr.AddNewlyCreatedDBObject(poly, true);
    
    // Create vertices
    Point3d[] points = new Point3d[]
    {
        new Point3d(0, 0, 0),
        new Point3d(10, 0, 0),
        new Point3d(10, 10, 0),
        new Point3d(0, 10, 0)
    };
    
    foreach (Point3d pt in points)
    {
        Vertex2d vertex = new Vertex2d(pt, 0, 0, 0, 0);
        poly.AppendVertex(vertex);
        tr.AddNewlyCreatedDBObject(vertex, true);
    }
    
    // Close the polyline
    poly.Closed = true;
    
    tr.Commit();
}

Example 2: Reading Polyline2d Vertices

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline2d poly = tr.GetObject(polylineId, OpenMode.ForRead) as Polyline2d;
    
    ed.WriteMessage($"\n=== Polyline2d Information ===");
    ed.WriteMessage($"\nType: {poly.PolyType}");
    ed.WriteMessage($"\nClosed: {poly.Closed}");
    ed.WriteMessage($"\nLength: {poly.Length:F3}");
    ed.WriteMessage($"\nElevation: {poly.Elevation:F3}");
    
    ed.WriteMessage("\n\nVertices:");
    int index = 0;
    
    foreach (ObjectId vertexId in poly)
    {
        Vertex2d vertex = tr.GetObject(vertexId, OpenMode.ForRead) as Vertex2d;
        
        ed.WriteMessage($"\n  Vertex {index}: ({vertex.Position.X:F2}, {vertex.Position.Y:F2})");
        ed.WriteMessage($"\n    Start Width: {vertex.StartWidth:F2}");
        ed.WriteMessage($"\n    End Width: {vertex.EndWidth:F2}");
        ed.WriteMessage($"\n    Bulge: {vertex.Bulge:F3}");
        
        index++;
    }
    
    tr.Commit();
}

Example 3: Modifying Polyline2d Vertices

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline2d poly = tr.GetObject(polylineId, OpenMode.ForRead) as Polyline2d;
    
    int index = 0;
    foreach (ObjectId vertexId in poly)
    {
        Vertex2d vertex = tr.GetObject(vertexId, OpenMode.ForWrite) as Vertex2d;
        
        // Set varying widths
        vertex.StartWidth = index * 0.5;
        vertex.EndWidth = (index + 1) * 0.5;
        
        index++;
    }
    
    tr.Commit();
}

Example 4: Creating a Polyline2d with Bulges (Arcs)

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Polyline2d poly = new Polyline2d();
    poly.SetDatabaseDefaults();
    
    btr.AppendEntity(poly);
    tr.AddNewlyCreatedDBObject(poly, true);
    
    // Create vertices with bulges for curved segments
    Point3d[] points = new Point3d[]
    {
        new Point3d(0, 0, 0),
        new Point3d(10, 0, 0),
        new Point3d(10, 10, 0),
        new Point3d(0, 10, 0)
    };
    
    double[] bulges = { 0.5, 0, -0.5, 0 }; // Positive = counterclockwise arc
    
    for (int i = 0; i < points.Length; i++)
    {
        Vertex2d vertex = new Vertex2d(points[i], 0, 0, 0, 0);
        vertex.Bulge = bulges[i];
        poly.AppendVertex(vertex);
        tr.AddNewlyCreatedDBObject(vertex, true);
    }
    
    poly.Closed = true;
    
    tr.Commit();
}

Example 5: Converting Polyline2d to Spline

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline2d poly = tr.GetObject(polylineId, OpenMode.ForWrite) as Polyline2d;
    
    // Convert to cubic spline
    poly.ConvertToPolylineType(Poly2dType.CubicSplinePoly);
    
    ed.WriteMessage($"\nConverted to: {poly.PolyType}");
    
    tr.Commit();
}

Example 6: Setting Polyline2d Properties

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline2d poly = tr.GetObject(polylineId, OpenMode.ForWrite) as Polyline2d;
    
    // Set properties
    poly.Layer = "Polylines";
    poly.ColorIndex = 3; // Green
    poly.Linetype = "DASHED";
    poly.LinetypeScale = 2.0;
    poly.LinetypeGenerationOn = true; // Continuous linetype through vertices
    
    // Set default widths
    poly.DefaultStartWidth = 0.5;
    poly.DefaultEndWidth = 0.5;
    
    // Set elevation and thickness
    poly.Elevation = 10.0;
    poly.Thickness = 2.0;
    
    tr.Commit();
}

Example 7: Inserting Vertices

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline2d poly = tr.GetObject(polylineId, OpenMode.ForWrite) as Polyline2d;
    
    // Insert a new vertex at index 1
    Vertex2d newVertex = new Vertex2d(new Point3d(5, 5, 0), 0, 0, 0, 0);
    newVertex.StartWidth = 0.25;
    newVertex.EndWidth = 0.25;
    
    poly.InsertVertexAt(1, newVertex);
    tr.AddNewlyCreatedDBObject(newVertex, true);
    
    ed.WriteMessage("\nInserted vertex at index 1");
    
    tr.Commit();
}

Example 8: Straightening a Polyline2d

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline2d poly = tr.GetObject(polylineId, OpenMode.ForWrite) as Polyline2d;
    
    ed.WriteMessage($"\nBefore straighten - Type: {poly.PolyType}");
    
    // Remove all curve fitting and bulges
    poly.Straighten();
    
    ed.WriteMessage($"\nAfter straighten - Type: {poly.PolyType}");
    
    tr.Commit();
}

Polyline2d Types

Type	Description
`SimplePoly`	Standard polyline with straight and arc segments
`FitCurvePoly`	Curve-fit polyline through vertices
`QuadSplinePoly`	Quadratic B-spline
`CubicSplinePoly`	Cubic B-spline

Vertex2d Properties

Property	Type	Description
`Position`	`Point3d`	Vertex location
`StartWidth`	`double`	Starting width at this vertex
`EndWidth`	`double`	Ending width at this vertex
`Bulge`	`double`	Arc bulge factor (0 = straight, ±1 = semicircle)
`TangentUsed`	`bool`	Whether tangent direction is used
`Tangent`	`double`	Tangent direction angle

Polyline vs Polyline2d

Feature	Polyline (Lightweight)	Polyline2d (Legacy)
Database Objects	Single object	Container + vertex objects
Memory Usage	Lower	Higher
Performance	Faster	Slower
Per-Vertex XData	No	Yes (each vertex is a DBObject)
3D Support	No	No (use Polyline3d)
Recommended	Yes (modern)	Only for compatibility

Best Practices

Use Lightweight Polyline: Prefer Polyline over Polyline2d for new drawings
Transaction Management: Remember to add both polyline and vertices to transaction
Vertex Ownership: Vertices are owned by the polyline and deleted with it
Bulge Calculation: Bulge = tan(angle/4), where angle is the included angle
Linetype Generation: Set LinetypeGenerationOn = true for continuous linetypes
Elevation: All vertices share the same elevation (Z coordinate)
Closed Polylines: Set Closed = true to connect last vertex to first
Width Variation: Use per-vertex widths for tapered segments

Common Use Cases

Legacy Drawing Compatibility: Reading/writing older DWG files
Per-Vertex Extended Data: When you need XData on individual vertices
Curve Fitting: Spline-fit polylines through control points
Variable Width Polylines: Tapered line segments

Related Objects

Polyline - Modern lightweight 2D polyline
Polyline3d - 3D polyline
Curve - Base class for polylines
Entity - Base class for all entities
Vertex2d - Individual vertex object

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Polyline2d Class

Overview

Namespace

Inheritance Hierarchy

Key Properties

Key Methods

Code Examples

Example 1: Creating a Polyline2d

Example 2: Reading Polyline2d Vertices

Example 3: Modifying Polyline2d Vertices

Example 4: Creating a Polyline2d with Bulges (Arcs)

Example 5: Converting Polyline2d to Spline

Example 6: Setting Polyline2d Properties

Example 7: Inserting Vertices

Example 8: Straightening a Polyline2d

Polyline2d Types

Vertex2d Properties

Polyline vs Polyline2d

Best Practices

Common Use Cases

Related Objects

References

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Polyline2d Class

Overview

Namespace

Inheritance Hierarchy

Key Properties

Key Methods

Code Examples

Example 1: Creating a Polyline2d

Example 2: Reading Polyline2d Vertices

Example 3: Modifying Polyline2d Vertices

Example 4: Creating a Polyline2d with Bulges (Arcs)

Example 5: Converting Polyline2d to Spline

Example 6: Setting Polyline2d Properties

Example 7: Inserting Vertices

Example 8: Straightening a Polyline2d

Polyline2d Types

Vertex2d Properties

Polyline vs Polyline2d

Best Practices

Common Use Cases

Related Objects

References