.. role:: blue
   :class: blue


MbLine3D Straight Line
======================
.. _MbLine3D_Straight_Line_:

.. kernel version: 

The :blue:`MbLine3D` class is declared in the *cur_line_3d.h* file. 

The :blue:`MbLine3D` straight line is described by the start point
:ref:`MbCartPoint3D <MbCartPoint3D_Radius_Vector_of_Point_in_3D_Space_>` **origin** and the direction vector
:ref:`MbVector3D <MbVector3D_Vector_in_Three-Dimensional_Space_>` **direction**. 

.. figure:: /MODELER/CURVES/pictures/O.4.2.1.png
   :width: 9cm
   :align: center


In the :blue:`PointOn`\( double & *t*, :blue:`MbCartPoint3D` & **r** ) method, the radius vector **r** of the line is described by the vector function 

.. math::

   \mathbf{r}(t) = \mathbf{origin} + t \cdot \mathbf{direction}.

The straight line behaves as an infinite object, although in its data it
has boundary values of the parameter *tmin* and
*tmax*. Note that, unlike other curves, in the methods
for calculating the radius vector and its derivatives the line does not
adjust the parameter *t* when it goes beyond the limiting values
*tmin* and *tmax*.