Polyline.md

Polyline Class

Overview

The Polyline class represents a lightweight 2D polyline in AutoCAD. It's an optimized version that uses less memory than the older Polyline2d class.

Namespace

Autodesk.AutoCAD.DatabaseServices

Inheritance Hierarchy

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

Key Properties

Property	Type	Description
NumberOfVertices	int	Gets the number of vertices
Closed	bool	Gets/sets whether the polyline is closed
Length	double	Gets the total length
Area	double	Gets the area (if closed)
Elevation	double	Gets/sets the elevation (Z value)
Normal	Vector3d	Gets/sets the normal vector
Thickness	double	Gets/sets the thickness
ConstantWidth	double	Gets/sets constant width for all segments
HasWidth	bool	Gets whether polyline has width
HasBulges	bool	Gets whether polyline has bulges (arcs)
Plinegen	bool	Gets/sets linetype generation mode

Key Methods

Method	Return Type	Description
AddVertexAt(int, Point2d, double, double, double)	void	Adds a vertex at specified index
RemoveVertexAt(int)	void	Removes vertex at index
GetPoint2dAt(int)	Point2d	Gets 2D point at vertex index
GetPoint3dAt(int)	Point3d	Gets 3D point at vertex index
SetPointAt(int, Point2d)	void	Sets point at vertex index
GetBulgeAt(int)	double	Gets bulge value at vertex
SetBulgeAt(int, double)	void	Sets bulge value at vertex
GetStartWidthAt(int)	double	Gets start width at segment
GetEndWidthAt(int)	double	Gets end width at segment
SetWidthsAt(int, double, double)	void	Sets start/end widths at segment
GetSegmentType(int)	SegmentType	Gets segment type (Line or Arc)

Code Examples

Example 1: Creating a Simple Polyline

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Polyline pline = new Polyline();
    
    // Add vertices
    pline.AddVertexAt(0, new Point2d(0, 0), 0, 0, 0);
    pline.AddVertexAt(1, new Point2d(100, 0), 0, 0, 0);
    pline.AddVertexAt(2, new Point2d(100, 50), 0, 0, 0);
    pline.AddVertexAt(3, new Point2d(0, 50), 0, 0, 0);
    
    // Close the polyline
    pline.Closed = true;
    
    btr.AppendEntity(pline);
    tr.AddNewlyCreatedDBObject(pline, true);
    
    tr.Commit();
}

Example 2: Creating Polyline with Bulges (Arcs)

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Polyline pline = new Polyline();
    
    // Add vertices with bulges
    // Bulge = tan(angle/4), where angle is the included angle
    // Bulge of 1 = 180° semicircle
    pline.AddVertexAt(0, new Point2d(0, 0), 0, 0, 0); // Straight segment
    pline.AddVertexAt(1, new Point2d(100, 0), 1, 0, 0); // Arc segment (bulge=1)
    pline.AddVertexAt(2, new Point2d(100, 100), 0, 0, 0); // Straight segment
    
    btr.AppendEntity(pline);
    tr.AddNewlyCreatedDBObject(pline, true);
    
    tr.Commit();
}

Example 3: Creating Polyline with Width

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Polyline pline = new Polyline();
    
    // Add vertices with varying widths
    pline.AddVertexAt(0, new Point2d(0, 0), 0, 5, 5); // Width 5
    pline.AddVertexAt(1, new Point2d(100, 0), 0, 5, 10); // Taper from 5 to 10
    pline.AddVertexAt(2, new Point2d(100, 100), 0, 10, 10); // Width 10
    
    btr.AppendEntity(pline);
    tr.AddNewlyCreatedDBObject(pline, true);
    
    tr.Commit();
}

Example 4: Iterating Through Polyline Vertices

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline pline = tr.GetObject(plineId, OpenMode.ForRead) as Polyline;
    
    int numVertices = pline.NumberOfVertices;
    
    for (int i = 0; i < numVertices; i++)
    {
        Point2d pt2d = pline.GetPoint2dAt(i);
        Point3d pt3d = pline.GetPoint3dAt(i);
        double bulge = pline.GetBulgeAt(i);
        SegmentType segType = pline.GetSegmentType(i);
        
        ed.WriteMessage($"\nVertex {i}: ({pt2d.X:F2}, {pt2d.Y:F2})");
        ed.WriteMessage($"\n  Bulge: {bulge:F4}");
        ed.WriteMessage($"\n  Segment Type: {segType}");
    }
    
    tr.Commit();
}

Example 5: Modifying Polyline Vertices

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline pline = tr.GetObject(plineId, OpenMode.ForWrite) as Polyline;
    
    // Move a vertex
    pline.SetPointAt(1, new Point2d(150, 50));
    
    // Add a new vertex
    pline.AddVertexAt(2, new Point2d(125, 75), 0, 0, 0);
    
    // Remove a vertex
    pline.RemoveVertexAt(0);
    
    // Set bulge for arc segment
    pline.SetBulgeAt(1, 0.5);
    
    tr.Commit();
}

Example 6: Getting Polyline Area and Length

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Polyline pline = tr.GetObject(plineId, OpenMode.ForRead) as Polyline;
    
    double length = pline.Length;
    double area = pline.Closed ? pline.Area : 0;
    
    ed.WriteMessage($"\nPolyline Length: {length:F2}");
    if (pline.Closed)
    {
        ed.WriteMessage($"\nPolyline Area: {area:F2}");
    }
    
    tr.Commit();
}

Common Patterns

Creating a Rectangle

Polyline rect = new Polyline();
rect.AddVertexAt(0, new Point2d(0, 0), 0, 0, 0);
rect.AddVertexAt(1, new Point2d(100, 0), 0, 0, 0);
rect.AddVertexAt(2, new Point2d(100, 50), 0, 0, 0);
rect.AddVertexAt(3, new Point2d(0, 50), 0, 0, 0);
rect.Closed = true;

Converting Line Segments to Polyline

// Assuming you have connected line segments
Polyline pline = new Polyline();
int index = 0;
foreach (Line line in lines)
{
    Point2d pt = new Point2d(line.StartPoint.X, line.StartPoint.Y);
    pline.AddVertexAt(index++, pt, 0, 0, 0);
}
// Add last endpoint
Point2d lastPt = new Point2d(lines.Last().EndPoint.X, lines.Last().EndPoint.Y);
pline.AddVertexAt(index, lastPt, 0, 0, 0);

Related Objects

• Polyline2d - Older 2D polyline format
• Polyline3d - 3D polyline
• Line - Single line segment
• Curve - Base class

References

• Autodesk Official Documentation