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Active Spline
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.. admonition:: Reference
   :class: refbox

   :Mode:      Edit Mode
   :Menu:      :menuselection:`Properties --> Curve --> Active Spline`

.. seealso:

   :doc:`Active Spline </modeling/curves/properties/active_spline>` for curves.

The *Active Spline* panel is used in Edit Mode to control properties of the currently selected spline.

.. figure:: /images/modeling_surfaces_properties_active-spline-panel.png
   :align: center

   Active Spline panel.

Cyclic U/V
   Like curves, surfaces can be closed (cyclical) or open, independently in both directions,
   allowing you to easily create a tube, donut or sphere shape,
   and they can be viewed as "solids" in *Edit Mode*.
   This can be set per interpolation axis.
Bézier U
   Makes the surface act like a Bézier curve.
   The control points act like *Free* handles of a Bézier curve.
   Depending on the *Order*, 3 or 4 control points form one spline segment.
   This can be set per interpolation axis.
   *Cyclic* and *Endpoint* must be disabled for this option to work.
Endpoint U/V
   Makes the surface contact the end control points.
   This can be set per interpolation axis.
   *Cyclic* must be disabled for this option to work.

   .. figure:: /images/modeling_surfaces_properties_endpoint.png
      :align: center
      :width: 50%

      Endpoint U.

   In the image below, the U interpolation axis is labeled as "U"
   and the V interpolation axis is labeled as "V".
   The U's interpolation axis has been set to *Endpoint*
   and as such the surface now extends to the outer edges from
   E1 to E2 along the U interpolation axis.

   To cause the surface to extend to all edges,
   *Endpoint* would be set for the V's axis as well.
Order U/V
   This property is the same as with :ref:`NURBS Curves <modeling-curve-order>`;
   it specifies how much the control points are taken into account for calculating the curve of the surface shape.
   For high Orders 1 the surface pulls away from the control points,
   creating a smoother surface by assuming that the *Resolution U/V* is high enough.
   For lowest Orders 2 the surface follows the control points,
   creating a surface that tends to follow the grid cage.

   .. _fig-surface-intro-order:

   .. figure:: /images/modeling_surfaces_properties_order.png
      :align: center
      :width: 50%

      Order 2 and Order 4 surface.

   For illustration purposes, in both Fig. :ref:`fig-surface-intro-order`,
   the knot vectors were set to *Endpoint*, causing the surface to extend to all edges.

   You can set independently the order for each interpolation axis,
   and like curves, it **cannot** be lower than 2,
   and higher than 6 or the number of control points on the relevant axis.
Resolution U/V
   Alters the :ref:`resolution <bpy.types.Curve.resolution_v>`
   of each segment by changing the number of subdivisions.
   This can be set per interpolation axis.
Smooth
   Use :ref:`Smooth Shading <modeling-meshes-editing-normals-shading>` for any 3D geometry.