This .NET class wraps the AcGeLine3d ObjectARX class. It represents an unbounded line in 3D space.

Autodesk.AutoCAD.Geometry.Entity3d
    Autodesk.AutoCAD.Geometry.Curve3d
        Autodesk.AutoCAD.Geometry.LinearEntity3d
            Autodesk.AutoCAD.Geometry.Line3d

Public sealed Class Line3d
Inherits LinearEntity3d

public sealed class Line3d : LinearEntity3d;