***********
Object Data
***********

The curve properties can be set from the *Object Data* tab
in the *Properties Header* (shown below in blue).

.. figure:: /images/modeling_curves_properties_header.png


Shape
=====

.. figure:: /images/modeling_curves_properties_curves-shape-panel.png

   Curves Shape panel.

Dimensions
   By default, new curves are set to be 3D, which means that control points can be placed anywhere in 3D space.
   Curves can also be set to 2D which constrain the control points to the curve's local XY axis.

   2D, 3D

.. _curve-resolution:

Resolution
   The *resolution* property defines the number of points that are computed between every pair of control points.
   Curves can be made more or less smooth by increasing and decreasing the resolution respectively.
   The *Preview U* setting determines the resolution in the 3D View while the *Render U* setting
   determines the curve's render resolution. If *Render U* is set to zero (0),
   then the *Preview U* setting is used for both the 3D View and render resolution.

   .. figure:: /images/modeling_curves_shape-resolution.jpg

      Curves with a resolution of 3 (left) and 12 (right).

Twisting
   A 3D curve has control points that are not located on the curve's local XY plane.
   This gives the curve a twist which can affect the curve normals.
   You can alter how the twist of the curve is calculated by choosing from *Minimum,
   Tangent* and *Z-Up* options from the select menu.

   .. figure:: /images/modeling_curves_shape-twist.jpg

      Curves with a twist of minimum (left) and tangent (right).

Fill
   Fill determines the way a curve is displayed when it is beveled (see below for details on Beveling).
   When set to *Half* (the default) the curve is displayed as half a cylinder.

   Fill Deformed
      Fills the curve after applying all modification that might deform the curve (i.e. shape keys and modifiers).

   .. figure:: /images/modeling_curves_shape-fill.jpg

      Curves with a fill of half (left) and full (right).

.. _curve-shape-path-curve-deform:

Path/Curve-Deform
   These options are primarily utilized when using a curve as a path or when using the Curve Deform Modifier.
   They control how objects use the curve and are dealt with in more detail in the appropriate links below.

   Radius
      Causes the deformed object to be scaled by the set curve radius.
   Stretch
      The *Stretch* curve option allows you to let the mesh object stretch, or squeeze, over the entire curve.
   Bounds Clamp
      ToDo.

.. seealso::

   - :doc:`/rigging/constraints/relationship/follow_path`
   - :doc:`/modeling/modifiers/deform/curve`


.. _curve-path-animation:

Path Animation
==============

The *Path Animation* settings can be used to determine how child objects move along a certain path.

Frames
   The number of frames that are needed to traverse the path,
   defining the maximum value for the *Evaluation Time* setting.
Evaluation Time
   Parametric position along the length of the curve that object following it should be at
   (the position is evaluated by dividing by the *Path Length* value).
   By default, it is linked to the global frame number,
   but could be keyframed to give more control over the path animation.
Follow
   Make the curve path children rotate along the curvature of the path.

.. note::

   Deprecated, but still available use.
   A more future-proof method is the :doc:`/rigging/constraints/relationship/follow_path`.


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

.. figure:: /images/modeling_curves_properties_active-spline-panel-curves.png

   Curves Active Spline panel.


The *Active Spline* panel becomes available during *Edit Mode*.

Cyclic
   Closes the curve.
Resolution
   Alters the smoothness of each segment by changing the number of subdivisions.
Interpolation
   Tilt
      Alters how the tilt of a segment is calculated.
   Radius
      Alters how the radius of a beveled curve is calculated.
      The effects are easier to see after Shrinking/Fattening a control point :kbd:`Alt-S`.
   Smooth
      Smooths the normals of the curve.


NURBS Curves
------------

.. figure:: /images/modeling_curves_properties_active-spline-panel-nurbs.png

   NURBS Active Spline panel.

.. _modeling-curve-knot:

Knots
   One of the characteristics of a NURBS object is the *knot vector*. This is a sequence of
   numbers used to determine the influence of the control points on the curve.
   While you cannot edit the knot vectors directly, you can influence them through the
   *Endpoint* and *Bézier* options in the Active Spline panel. Note that the
   *Endpoint* and *Bézier* settings only apply to open NURBS curves.

   Cyclic
      Makes the NURBS curve cyclic.

      .. figure:: /images/modeling_curves_nurbs-cyclic.png

         A NURBS curve with Cyclic applied.

   Bézier
      Makes the NURBS curve act like a Bézier curve.
   Endpoint
      Makes the curve contact the end control points. Cyclic must be disabled for this option to work.

      .. figure:: /images/modeling_curves_nurbs-endpoint.png

         A NURBS curve with Endpoint enabled.

.. _modeling-curve-order:

Order
   The order of the NURBS curve determines the area of influence of the control points over the curve.
   Higher order values means that a single control point has a greater
   influence over a greater relative proportion of the curve.
   The valid range of *Order* values is 2-6 depending on the number of control points present in the curve.

   .. figure:: /images/modeling_curves_nurbs-order.png

      NURBS curves with orders of 2 (left), 4 (middle) and 6 (right).