Mike Williams wrote:

> Wasn't it Retsam who wrote:
>>Tyler Eaves wrote:
>>>
>>>Should produce a perfect 180 curve, with straght lines entering and
>>>exiting. The final goal of the project is to render a rollercoaster
>>>design, so smooth curves are a must!
>>>
>>
>>Actually, that wouldn't be the "smoothest" curve.  Going from straight to
>>a
>>sharp curve without any transition is not smooth.  Going from a curve to
>>straight without a transition is not smooth.  People in a roller coaster
>>would definitely feel like they were being jerked around at the
>>transitions.  Literally.  You would have an infinite 3rd derivative at the
>>transitions.  And in technical circles, the the third derivative is called
>>"jerk".
>>
>>0th derivative: position
>>1st derivative: velocity
>>2nd derivative: acceleration
>>3rd derivative: jerk
> 
> Actually, for rollercoasters, the 4th derivative has a significant
> effect on the tendency of the passengers to vomit. It's called "jounce".
> 
> I believe that Retsam's problem is that if he doesn't specify the spline
> type, then it defaults to "linear_spline". He needs to specify one of
> the other spline types.
> 

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!

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