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2 May 2025 04:30:23 EDT (-0400)
  profile following a parametric curve (Message 1 to 7 of 7)  
From: kurtz le pirate
Subject: profile following a parametric curve
Date: 1 May 2025 06:22:42
Message: <68134b72@news.povray.org>
hello,


My first attempts.

Curves are defined with Cartesian parameters: x=f(t), z=g(t).
The profile is a simple polygon.

Basic texture, lighting with area_light.
Low resolution (800x600).








-- 
kurtz le pirate
compagnie de la banquise


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Attachments:
Download 'param_limaconofpascal .png' (75 KB) Download 'param_hypotrochoidet.png' (173 KB) Download 'param_lemniscateofbernoulli.png' (86 KB)

Preview of image 'param_limaconofpascal .png'
param_limaconofpascal .png

Preview of image 'param_hypotrochoidet.png'
param_hypotrochoidet.png

Preview of image 'param_lemniscateofbernoulli.png'
param_lemniscateofbernoulli.png


 

From: Bald Eagle
Subject: Re: profile following a parametric curve
Date: 1 May 2025 08:40:00
Message: <web.68136b97174259626563700825979125@news.povray.org>
kurtz le pirate <kur### [at] freefr> wrote:

> Curves are defined with Cartesian parameters: x=f(t), z=g(t).
> The profile is a simple polygon.

Nice job with the profiles.

What's the arc-length of that lemniscate?   :D

- BE


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From: kurtz le pirate
Subject: Re: profile following a parametric curve
Date: 1 May 2025 09:53:55
Message: <68137cf3@news.povray.org>
On 01/05/2025 14:39, Bald Eagle wrote:
> kurtz le pirate <kur### [at] freefr> wrote:
> 
>> Curves are defined with Cartesian parameters: x=f(t), z=g(t).
>> The profile is a simple polygon.
> 
> Nice job with the profiles.
> 
> What's the arc-length of that lemniscate?   :D


Simple. Here, half-width a = 24 = c√2.

                   2*π
Then, length = --------- * c
                M(1,1/√2)


With M(a,b) the arithmetic–geometric mean function.


;)




-- 
kurtz le pirate
compagnie de la banquise


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From: William F Pokorny
Subject: Re: profile following a parametric curve
Date: 1 May 2025 10:34:16
Message: <68138668$1@news.povray.org>
On 5/1/25 06:22, kurtz le pirate wrote:
> My first attempts.
> 
> Curves are defined with Cartesian parameters: x=f(t), z=g(t).
> The profile is a simple polygon.

Cool!

Bill P.


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From: Bald Eagle
Subject: Re: profile following a parametric curve
Date: 1 May 2025 11:40:00
Message: <web.6813953c174259626563700825979125@news.povray.org>
kurtz le pirate <kur### [at] freefr> wrote:

> Simple. Here, half-width a = 24 = c√2.
>
>                    2*π
> Then, length = --------- * c
>                 M(1,1/√2)
>
>


Maybe not so simple?
https://en.wikipedia.org/wiki/Elliptic_function#History

(I only know that because I was trying to hunt down a good overview of
calculating the arc-length of a catenary, and move along the curve at regular
intervals.)

- BW


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From: kurtz le pirate
Subject: Re: profile following a parametric curve
Date: 1 May 2025 12:01:32
Message: <68139adc$1@news.povray.org>
On 01/05/2025 17:37, Bald Eagle wrote:
> kurtz le pirate <kur### [at] freefr> wrote:
> 
>> Simple. Here, half-width a = 24 = c√2.
>>
>>                     2*π
>> Then, length = --------- * c
>>                  M(1,1/√2)
>>
>>
>> With M(a,b) the arithmetic–geometric mean function.
> 
> Maybe not so simple?
> https://en.wikipedia.org/wiki/Elliptic_function#History


That's right.

But my answer is more of a joke and a simple copy/paste from Wiki
<https://en.wikipedia.org/wiki/Lemniscate_of_Bernoulli#Arc_length_and_elliptic_functions>








-- 
kurtz le pirate
compagnie de la banquise


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From: Bald Eagle
Subject: Re: profile following a parametric curve
Date: 1 May 2025 12:45:00
Message: <web.6813a418174259626563700825979125@news.povray.org>
kurtz le pirate <kur### [at] freefr> wrote:

> That's right.
>
> But my answer is more of a joke and a simple copy/paste from Wiki
>
<https://en.wikipedia.org/wiki/Lemniscate_of_Bernoulli#Arc_length_and_elliptic_functions>


Nice.  (I suspected)

"It therefore obviously follows that . . ."    ;)

- BW


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