RailwayRouteOptimization/scripts/Draw/Circle/CircleCP/doc/CircleCP_proc_en.html

<ol>
  <li>Set the center of the circle using the mouse or enter a coordinate in the
  command line.</li>
  <li>Define the radius by clicking a point on the circle line or by entering a
  coordinate into the command line. You may also enter the radius in the
  command line.</li>
</ol>