.. role:: blue
   :class: blue

MbEdge Edge
===========
.. _MbEdge_Edge_:

.. kernel version: 

The :blue:`MbEdge` class is declared in the *topology.h* file.

The MbEdge edge is a derived class of the :blue:`MbTopologyItem`
topological object and represents a curve with an assigned direction.
The direction of the :blue:`MbCurve3D` curve is strictly linked to the
direction of increase of its parameter. Unlike a curve, an edge can be
directed both in the direction of increasing the parameter and in the
direction of decreasing the curve parameter. An edge always starts and
ends at some :ref:`MbVertex <MbVertex_Vertex_>` vertex.

The edge data structure contains a pointer to the curve
:blue:`MbCurve3D` **curve**, a flag indicating coincidence of the
edge direction with the curve direction *sameSense*, a pointer to the
start vertex :blue:`MbVertex` **begVertex**, and a pointer to the end
vertex :blue:`MbVertex` **endVertex**. Fig. 1 shows an edge.

.. figure:: /MODELER/TOPOLOGICAL_OBJECTS/pictures/O.7.3.1.png
   :width: 15cm
   :align: center

   Fig. 1

Pointers to the curve and vertices cannot be null. The flag indicating
coincidence of the edge direction with the curve direction is set to
true if the edge coincides with the curve, and to false if the edge is
directed opposite to the curve. If an edge starts and ends at the same
vertex, then such an edge is closed. Pointers to the start and end
vertex of a closed edge are equal.

The edge can be named and can have attributes. The name can be used to
identify the edge, and attributes can carry additional information about
the edge, such as color, display style, origin, and so on.

The edge is used for wireframe modeling.