RailwayRouteOptimization/scripts/Draw/Spline/SplineControlPoints/doc/SplineControlPoints_proc_en.html

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  <ol>
    <li>Choose the degree of the spline in the options tool bar. Supported
    degrees are 2 (quadratic b-spline) and 3 (cubic b-spline). The higher the
    degree, the 'smoother' the curve becomes. 
    <br />Note that a quadratic b-spline requires by definition at least 3
    control points while a cubic b-spline has at least 4 control points.</li>
    <li>Check the 'Closed' check box in the options tool bar if you want to
    create a closed spline. Closed splines are continuous closed loops.</li>
    <li>Specify the control points. After defining the third (for quadratic
    b-splines) or fourth (for cubic b-splines) control point, a preview will be
    shown. You can remove the last control point again by clicking the 'Undo'
    button in the options tool bar.</li>
    <li>Hit escape or click the right mouse button after setting the last point
    to confirm the spline shape.</li>
    <li>You can now create another spline or right-click again to terminate the
    tool.</li>
  </ol>
  <p>Example for two open splines (quadratic and cubic): 
  <br />
  <img src="SplineControlPoints01.png" class="figure" />
  <br />Example for two closed, periodic splines (quadratic and cubic): 
  <br />
  <img src="SplineControlPoints02.png" class="figure" /></p>
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