Tyler Eaves <tyl### [at] hotpopcom> wrote in news:3e8b2a30@news.povray.org:

... 
> No I just didn't give a spline type because I didn't want to imply
> which one I was using. Perhaps I was misleading by saying smooth. What
> I mean was more constant radius. The ride style I'm looking to emulate
> are the older style steel coasters. The manufacuters at the time were
> limited to constant radius curves, such as in the following picture:
> 
> http://rcdb.com/installationgallery224.htm?Picture=2
> 
> The train enters the boomerang element, each half of which is made up
> of three seperate curves, the half corkscrew, the first 90 degrees of
> the half loop, then the bottom. Three distinct radii. I could kinda
> get there with a natural spline with addiontal points, but for
> instance in the hypothetical curve I mentioned above, you get a small
> 's' shape at the entrance and exit, definatly NOT smooth, and
> definatly WEIRD! 

You will need rational splines in order to obtain
perfect circle segments for your track. And AFAIK
the spline types implemented in POV-Ray does not
currently include rational splines. But it can be
implemented with macros in scripts.

If you can tolerate some small errors, then you can
"string" together many smaller splines segments to
form a circle segment.

I once mad a kind of rollercoaster like track by
splicing together several lathe "segments".

To see an image of this, look for my post:

"Twisted Lathe (35 KB)"
3. June 2000 in povray.binaries.images
 
http://news.povray.org/povray.binaries.images/12302/


This post may also be of interest:

http://news.povray.org/povray.binaries.images/14118/

"Joining cylinders smootly (10KB)"
3. July 2001 in povray.binaries.images


Tor Olav

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