This .NET class wraps the AcGeRay3d ObjectARX class. It represents a half-bounded line in 3D space. A Ray3d object either has a start point but no endpoint, or has an endpoint but no start point.

Autodesk.AutoCAD.Geometry.Entity3d
    Autodesk.AutoCAD.Geometry.Curve3d
        Autodesk.AutoCAD.Geometry.LinearEntity3d
            Autodesk.AutoCAD.Geometry.Ray3d

Public sealed Class Ray3d
Inherits LinearEntity3d

public sealed class Ray3d : LinearEntity3d;