"Marina" <mbr### [at] huskersunledu> wrote:
> I am trying to create the symbol to show circular polarization for a physics
> diagram so I need an arrow in the shape of a circle. However, the only way I can
> currently do it is to just make a circle and add a cone in one section... what I
> want is a slight gap between the head and tail of the arrow so it's not all just
> one continuous object. I haven't figured out how to use the features of POV-Ray
> that let you 'take away' from objects. Could anyone show me what the easiest way
> to go about this would be? At least point me in the right direction? I'd really
> appreciate it.
> Thanks! :)

"Marina" <mbr### [at] huskersunledu> wrote:
> I am trying to create the symbol to show circular polarization for a physics
> diagram so I need an arrow in the shape of a circle. However, the only way I can
> currently do it is to just make a circle and add a cone in one section... what I
> want is a slight gap between the head and tail of the arrow so it's not all just
> one continuous object. I haven't figured out how to use the features of POV-Ray
> that let you 'take away' from objects. Could anyone show me what the easiest way
> to go about this would be? At least point me in the right direction? I'd really
> appreciate it.
> Thanks! :)


I think you just need to read up on the difference statement.   Make your cone.
Make your torus.  Make another object - a box or something to cut away the shape
you want to remove from the torus.   Then combine the code for the box (or
whatever) and the torus into a difference statement:

http://www.povray.org/documentation/view/3.6.1/306/

This is from Pov-Ray for Windows's "Insert" menu:

// CSG difference, subtract intersections of shapes 2...N from Shape1
difference {
  Shape1 {...} // Start with this shape
  Shape2 {...} // This will be "cut out" of Shape1
  ShapeN {...} // This will be "cut out" of Shape1
}


On the other hand, does it have to be a cone and a torus?   You might also look
into prisms.  Maybe make a closed linear 2D spline, and use it as the basis of
your prism.... to extrude it to 3D.   Then you could have a nicely shaped tail
on it.  (Using a linear spline, as opposed to some other type of spline would
make it easy to create sharp corners and angles.)

Charles

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