CenterStage Object Class: Tube Subclass of: SurfaceFormCurve Requires reference to a Curve object The Tube class lets you create a tube around an existing Curve object. By default, the tube is circular of constant radius, but you can make it any shape you want, and the radius can vary along the curve. The second parameter for the surface is used as the parameter along the reference curve, while the first parameter of the surface is used to generate the shape for the tube. This tube shape is expressed in the Frenet frame of the reference curve, in absolute coordinates. The Tube class supports all the directives of the SurfaceFromCurve class (except for the Function directive), plus the following: Tube param func [-frame | -absolute] Here "param" specifies the parameter that forms the shape of the tube, and the "func" is an expression that returns the coordinates of a point on the tube, relative to a point on the reference curve. If -frame is specified (the default), then "func" should produce an ordered pair that represents a position in the normal-binormal plane. If -absolute is specified, then the function should produce a point in absolute coordinates (with the point on the curve as the origin). For example: Tube {theta} {(2cos(theta), sin(theta))} produces an oval tube using the Frenet frame, while Tube {s} {(cos(s),sin(s),0)} -absolute produces a circular tube, but the circles all lie parallel to the xy-plane. Note that "func" is not a TCL script, but an expression. If you need to do more complicated computations, you can call a TCL procedure as follows: Tube {s} {myTube(s)} -absolute vproc myTube {s} { if {\$s < \$pi} {let P = (2s,0,s^2)} \ else {let P = (s,s,2s)} return \$P } While the tube shape usually is independent of the position along the curve, you may want to make your tube depend on the curve's parameter as well. In this case, you can specify two parameters, and the second is the one used by the curve: Tube {s t} { (cos(t),-sin(t), sin(t), cos(t)) * (sin(2s),cos(s)) } This example forms a figure-8 tube that rotates as it moves along the curve. Radius r This directive specifies the radius of the tube. After the tube function is computed, it is multiplied by this value in order to obtain the final tube position. You can use an expression for the radius, and the expression can include the parameter for the curve. For example: Radius {sqrt(1+t^2)} where t is the parameter listed in the Function directive of the reference curve.