POV-Ray : Newsgroups : povray.advanced-users : Exponential cylinder density function Server Time
30 Jul 2021 23:10:59 EDT (-0400)
  Exponential cylinder density function (Message 1 to 8 of 8)  
From: Mike Horvath
Subject: Exponential cylinder density function
Date: 6 Feb 2021 23:48:34
Message: <601f7122$1@news.povray.org>
I am using this density function:

function {1-f_cylindrical(x,y,z)}

How do I make it so that the density decreases exponentially?

Simply this?

function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}

Thanks.


Mike


Post a reply to this message

From: Mike Horvath
Subject: Re: Exponential cylinder density function
Date: 6 Feb 2021 23:49:50
Message: <601f716e$1@news.povray.org>
On 2/6/2021 11:48 PM, Mike Horvath wrote:
> I am using this density function:
> 
> function {1-f_cylindrical(x,y,z)}
> 
> How do I make it so that the density decreases exponentially?
> 
> Simply this?
> 
> function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}
> 
> Thanks.
> 
> 
> Mike


Increases rather.


Mike


Post a reply to this message

From: Bald Eagle
Subject: Re: Exponential cylinder density function
Date: 7 Feb 2021 09:10:09
Message: <web.601ff42ce7960e541f9dae300@news.povray.org>
Mike Horvath <mik### [at] gmailcom> wrote:
> On 2/6/2021 11:48 PM, Mike Horvath wrote:
> > I am using this density function:
> >
> > function {1-f_cylindrical(x,y,z)}
> >
> > How do I make it so that the density decreases exponentially?
> Increases rather.


> > function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}

This would be geometrically?

Exponentially would imply using log() or (exp) ?
or maybe pow (term, some varying power)

I usually use a spreadsheet, or plot my function in POV-Ray with spheres to show
myself what's actually going on


Post a reply to this message

From: Alain Martel
Subject: Re: Exponential cylinder density function
Date: 8 Feb 2021 10:24:57
Message: <602157c9$1@news.povray.org>
Le 2021-02-07 à 09:07, Bald Eagle a écrit :
> 
> Mike Horvath <mik### [at] gmailcom> wrote:
>> On 2/6/2021 11:48 PM, Mike Horvath wrote:
>>> I am using this density function:
>>>
>>> function {1-f_cylindrical(x,y,z)}
>>>
>>> How do I make it so that the density decreases exponentially?
>> Increases rather.
> 
> 
>>> function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}
> 
> This would be geometrically?
> 
> Exponentially would imply using log() or (exp) ?
> or maybe pow (term, some varying power)
> 
> I usually use a spreadsheet, or plot my function in POV-Ray with spheres to show
> myself what's actually going on
> 
> 

function {1-f_cylindrical(x,y,z)*f_cylindrical(x,y,z)}
is exactly the same as
function {1-pow(f_cylindrical(x,y,z),2)}

The advantage of the second is that f_cylindrical need to be evaluated 
only once, making the evaluation of the whole function faster.

An exponential curve could be something like :
function {1- exp(f_cylindrical(x,y,z))}


Post a reply to this message

From: Mike Horvath
Subject: Re: Exponential cylinder density function
Date: 8 Feb 2021 16:22:25
Message: <6021ab91$1@news.povray.org>
On 2/7/2021 9:07 AM, Bald Eagle wrote:
> This would be geometrically?
> 

Dunno what you mean.

> Exponentially would imply using log() or (exp) ?
> or maybe pow (term, some varying power)
> 
> I usually use a spreadsheet, or plot my function in POV-Ray with spheres to show
> myself what's actually going on
> 
> 

Which would be better for planet atmosphere density? I used `pow` but is 
`exp` better?


Mike


Post a reply to this message

From: Mike Horvath
Subject: Re: Exponential cylinder density function
Date: 8 Feb 2021 16:24:04
Message: <6021abf4$1@news.povray.org>
On 2/8/2021 10:24 AM, Alain Martel wrote:
> The advantage of the second is that f_cylindrical need to be evaluated 
> only once, making the evaluation of the whole function faster.
> 

Good tip, thanks! Any speed improvement is important.


Mike


Post a reply to this message

From: Bald Eagle
Subject: Re: Exponential cylinder density function
Date: 8 Feb 2021 18:55:01
Message: <web.6021ced0e7960e541f9dae300@news.povray.org>
Mike Horvath <mik### [at] gmailcom> wrote:
> On 2/7/2021 9:07 AM, Bald Eagle wrote:
> > This would be geometrically?
> Dunno what you mean.

Doesn't matter - I think they're the same.


> Which would be better for planet atmosphere density? I used `pow` but is
> `exp` better?

https://en.wikipedia.org/wiki/Density_of_air#Variation_with_altitude


Post a reply to this message

From: Mike Horvath
Subject: Re: Exponential cylinder density function
Date: 22 Feb 2021 13:57:50
Message: <6033feae$1@news.povray.org>
On 2/8/2021 6:52 PM, Bald Eagle wrote:
> Mike Horvath <mik### [at] gmailcom> wrote:
>> On 2/7/2021 9:07 AM, Bald Eagle wrote:
>>> This would be geometrically?
>> Dunno what you mean.
> 
> Doesn't matter - I think they're the same.
> 
> 
>> Which would be better for planet atmosphere density? I used `pow` but is
>> `exp` better?
> 
> https://en.wikipedia.org/wiki/Density_of_air#Variation_with_altitude
> 
> 
> 
> 

I'm not very good at math so I don't know how to translate that into 
something POV-Ray can consume.


Mike


Post a reply to this message

Copyright 2003-2021 Persistence of Vision Raytracer Pty. Ltd.