**********
Properties
**********

.. figure:: /images/modeling_surfaces_properties_nurbs.png

   Surface Properties.

The panels of the *Curve and Surface* tab are the same as for
:doc:`curves </modeling/curves/introduction>`, just with fewer options...


Shape
=====

.. figure:: /images/modeling_surfaces_properties_resolution-panel.png

   Shape panel.

You can adjust the resolution separately for both preview and render,
to not slow things down in the viewport, but still get good render results.

Preview
   U, V
Render
   U, V


Active Spline
=============

Closed and Open Surfaces
------------------------

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 drawn as "solids" in *Edit Mode*.
This makes working with surfaces quite easy.


Bézier, Endpoint
----------------

Just like :ref:`NURBS curves <modeling-curve-knot>`, NURBS surfaces have two knot vectors,
one for each U and V axis. Here again, they can be one of *Cyclic*, *Endpoint*,
or *Bézier*, with the same properties as for curves. And as with curves, only open surfaces
(in the relevant direction) are affected by this setting...

.. _fig-surface-intro-endpoint:

.. figure:: /images/modeling_surfaces_properties_endpoint.png

   Endpoint U.

In Fig. :ref:`fig-surface-intro-endpoint` 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 you would set the V's axis to
*Endpoint* as well.


Order
-----

One more time, 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`_ 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

   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
----------

Just like :ref:`NURBS curves <curve-nurbs>`, *Resolution* controls the detail of the surface.
The higher the *Resolution* the more detailed and smoother the surface is.
The lower the *Resolution* the rougher the surface. However, here you have two resolution settings,
one for each interpolation axis (U and V). Note that unlike with curves, you have only one resolution
(the *Resolution* U and V fields, in the *Curve Tools* panel)...

.. list-table::

   * - .. figure:: /images/modeling_surfaces_properties_resolution-1x1-wire.png

     - .. figure:: /images/modeling_surfaces_properties_resolution-3x3-wire.png

   * - .. _fig-surface-intro-resolution1:

       .. figure:: /images/modeling_surfaces_properties_resolution-1x1.png

          Resolution 1×1.

     - .. _fig-surface-intro-resolution2:

       .. figure:: /images/modeling_surfaces_properties_resolution-3x3.png

          Resolution 3×3.

Fig. :ref:`fig-surface-intro-resolution1` is an example of a surface resolution of 1 for both U and V.
Fig. :ref:`fig-surface-intro-resolution2` surface is an example of a surface resolution of 3 for both U and V.


Smooth
------

Use :ref:`Smooth Shading <modeling-meshes-editing-normals-shading>`.