Line.md

Line Class

Overview

The Line class represents a straight line segment in AutoCAD. It is one of the most fundamental geometric entities, defined by two endpoints.

Namespace

Autodesk.AutoCAD.DatabaseServices

Inheritance Hierarchy

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

Key Properties

Property	Type	Description
StartPoint	Point3d	Gets/sets the start point of the line
EndPoint	Point3d	Gets/sets the end point of the line
Delta	Vector3d	Gets the vector from start to end point
Length	double	Gets the length of the line
Angle	double	Gets the angle of the line in radians
Normal	Vector3d	Gets/sets the normal vector
Thickness	double	Gets/sets the thickness (for 3D extrusion)

Key Methods

Method	Return Type	Description
GetClosestPointTo(Point3d, bool)	Point3d	Gets the closest point on the line to a given point
GetDistAtPoint(Point3d)	double	Gets the distance along the line to a point
GetPointAtDist(double)	Point3d	Gets a point at a specified distance along the line
GetPointAtParameter(double)	Point3d	Gets a point at a parameter value (0-1)

Code Examples

Example 1: Creating a Line

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 a line from (0,0,0) to (100,100,0)
    Line line = new Line(new Point3d(0, 0, 0), new Point3d(100, 100, 0));
    
    // Set properties
    line.Layer = "0";
    line.ColorIndex = 1; // Red
    
    // Add to database
    btr.AppendEntity(line);
    tr.AddNewlyCreatedDBObject(line, true);
    
    tr.Commit();
}

Example 2: Modifying Line Endpoints

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Line line = tr.GetObject(lineId, OpenMode.ForWrite) as Line;
    
    // Move the start point
    line.StartPoint = new Point3d(10, 10, 0);
    
    // Move the end point
    line.EndPoint = new Point3d(200, 150, 0);
    
    tr.Commit();
}

Example 3: Getting Line Properties

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Line line = tr.GetObject(lineId, OpenMode.ForRead) as Line;
    
    double length = line.Length;
    double angle = line.Angle * (180.0 / Math.PI); // Convert to degrees
    Vector3d direction = line.Delta.GetNormal(); // Normalized direction vector
    
    Point3d midPoint = line.GetPointAtParameter(0.5); // Midpoint
    
    ed.WriteMessage($"\nLine Length: {length:F2}");
    ed.WriteMessage($"\nLine Angle: {angle:F2}°");
    ed.WriteMessage($"\nMidpoint: ({midPoint.X:F2}, {midPoint.Y:F2})");
    
    tr.Commit();
}

Example 4: Finding Closest Point on Line

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Line line = tr.GetObject(lineId, OpenMode.ForRead) as Line;
    
    Point3d testPoint = new Point3d(50, 75, 0);
    
    // Get closest point on line (extend = false means don't extend beyond endpoints)
    Point3d closestPoint = line.GetClosestPointTo(testPoint, false);
    
    double distance = testPoint.DistanceTo(closestPoint);
    
    ed.WriteMessage($"\nClosest point: ({closestPoint.X:F2}, {closestPoint.Y:F2})");
    ed.WriteMessage($"\nDistance: {distance:F2}");
    
    tr.Commit();
}

Example 5: Creating Multiple Lines (Rectangle)

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    Point3d p1 = new Point3d(0, 0, 0);
    Point3d p2 = new Point3d(100, 0, 0);
    Point3d p3 = new Point3d(100, 50, 0);
    Point3d p4 = new Point3d(0, 50, 0);
    
    // Create four lines forming a rectangle
    Line[] lines = new Line[]
    {
        new Line(p1, p2),
        new Line(p2, p3),
        new Line(p3, p4),
        new Line(p4, p1)
    };
    
    foreach (Line line in lines)
    {
        btr.AppendEntity(line);
        tr.AddNewlyCreatedDBObject(line, true);
    }
    
    tr.Commit();
}

Common Patterns

Creating a Line at an Angle

Point3d startPoint = new Point3d(0, 0, 0);
double length = 100.0;
double angleInDegrees = 45.0;
double angleInRadians = angleInDegrees * (Math.PI / 180.0);

Point3d endPoint = new Point3d(
    startPoint.X + length * Math.Cos(angleInRadians),
    startPoint.Y + length * Math.Sin(angleInRadians),
    startPoint.Z
);

Line line = new Line(startPoint, endPoint);

Extending a Line

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Line line = tr.GetObject(lineId, OpenMode.ForWrite) as Line;
    
    // Extend by 10 units in the direction of the line
    Vector3d direction = line.Delta.GetNormal();
    line.EndPoint = line.EndPoint + (direction * 10.0);
    
    tr.Commit();
}

Related Objects

• Curve - Base class for Line
• Entity - Base class for all entities
• Polyline - Multiple connected line segments
• Arc - Curved counterpart to Line

References

• Autodesk Official Documentation