POV-Ray : Newsgroups : povray.text.scene-files : Tangents between circles : Re: Tangents between circles Server Time
24 Oct 2021 02:47:06 EDT (-0400)
  Re: Tangents between circles  
From: Bald Eagle
Date: 26 Dec 2019 20:20:00
Message: <web.5e055c201b345bf54eec112d0@news.povray.org>
"jr" <cre### [at] gmailcom> wrote:

> phew, and I'm floundering..  :-(  cannot see how you've arrived at the data in
> 'CircleArray' elements 6 + 8/9.

An initial circle array should have everything defined with _All or _Both to
render a starting image to starting picking tangents and arcs.

> (part of the confusion is that calculations and representation are so
> intertwined, like when you use a colour ([n][6]) to select a tangent.  and what
> is special about the order of indices in 'TangentList'?)

All of the calculations should be nice and neat and tidy in the upper part of
the scene file. BezierArcs and analyticalTangents

The TangentList array takes the [named] numerical values that you use to select
the colored tangent lines and "converts"/indexes that to which tangents in the
AnalyticalTangent macro output array they correspond to.

> choice of tangents and which part of
> circumference to draw should be derived.

I had this idea in mind - but it's never going to be quite that simple, and the
logic involved in doing that ---- it's going to be challenging.   I had started
to look into serpentine belt design software to see if I could deivine some
rules or see some code ---- but that is a LONG tangent [sic] that I thought best
not to pursue.  "Get the PRISM rendered." was the goal - and that took a mighty

> well, that is the idea(l).  Q - can you provide guidance, please?

Well, you'd have to flowchart it out and see what happens.  What happens if the
circles aren't laid out in the array just like that?  What happens if they
overlap or one is inside the other (just by mistake).  How do you determine
which tangent is the "outside" one - to give you the intended, desired "convex
hull" truncated/rounded triangle that we're talking about?  That seemed like an
unnecessary mountain to climb over.

> this is just for drawing prisms, getting an understanding, really; ignore
> pulleys for now.
> and one more question, a prism made using just two circles, will that be doable
> (wrt comment above 'ArrayIsLinear')?

That was the idea.  I put that in there when considering just that - but I don't
know if I tested that out and saw if it worked properly or not.

Got some residual holiday / RL stuff to get out of the way and hopefully I willl
have a block of uninterrupted time and enough of an energy spurt to make another
meaningful contribution to this.
I would also like to see what Leroy has come up with - I'm not sure if his stuff
only runs under Windows or what...

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