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29 Jul 2024 10:30:31 EDT (-0400)
  Using slope on spheres (Message 1 to 3 of 3)  
From: David Given
Subject: Using slope on spheres
Date: 10 Jul 2011 17:22:30
Message: <4e1a1816$1@news.povray.org>
I'm rendering the moon:

http://code.google.com/p/flooded-moon/

One thing that needs improving is the texture used for the landscape.
For example, in the linked animation, Mons Huygens rises about four and
a half *kilometres* above sea level in a very short distance, but
without decent visual cues as to the steepness of the slope the size
isn't apparent and it just looks odd.

It looks like the Povray slope function would be ideal for this as it
will do everything automatically; but the slope function assumes a flat
world with a fixed up vector. My world is spherical, which means the up
vector changes depending where you are on the surface.

Does anyone know of any cunning ways to let me use slope on my moon and
have it work correctly?

-- 
┌─── dg@cowlark.com ─────
http://www.cowlark.com ─────
│
│ "I have a mind like a steel trap. It's rusty and full of dead mice."
│ --- Anonymous, on rasfc


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From: Le Forgeron
Subject: Re: Using slope on spheres
Date: 10 Jul 2011 19:09:10
Message: <4e1a3116@news.povray.org>
Le 10/07/2011 23:22, David Given nous fit lire :
> I'm rendering the moon:
> 
> http://code.google.com/p/flooded-moon/
> 
> One thing that needs improving is the texture used for the landscape.
> For example, in the linked animation, Mons Huygens rises about four and
> a half *kilometres* above sea level in a very short distance, but
> without decent visual cues as to the steepness of the slope the size
> isn't apparent and it just looks odd.
> 
> It looks like the Povray slope function would be ideal for this as it
> will do everything automatically; but the slope function assumes a flat
> world with a fixed up vector. My world is spherical, which means the up
> vector changes depending where you are on the surface.
> 
> Does anyone know of any cunning ways to let me use slope on my moon and
> have it work correctly?
> 
slope of 3.7 with point_at
(using the center of your world)

> http://wiki.povray.org/content/Documentation:Reference_Section_5.5#Quilted


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From: David Given
Subject: Re: Using slope on spheres
Date: 11 Jul 2011 15:29:46
Message: <4e1b4f2a@news.povray.org>
On 11/07/11 00:09, Le_Forgeron wrote:
[...]
> slope of 3.7 with point_at
> (using the center of your world)

Thanks --- that works beautifully! And I'm using a 3.7 release candidate
anyway...

https://lh6.googleusercontent.com/-VrONBXhKp30/ThtN9q36zaI/AAAAAAAAAVw/S1kBVA5Us8o/s800/map.png

This is an image of Mons Huygens (my favourite test area) Map mode.
Contours are 500m at each transition. Relief shading is done with the
slope function.

Interestingly, at this scale the pixels in my underlying topographic
data are quite large, and my first attempt to use slope shading showed
hideous blockiness: the first-differential effect of the slope function
was neatly undoing the bilinear scaling. Luckily, switching to bicubic
shading (also new in 3.7) produced the results you can see above.

Now to switch back to my exterior model and see if I can improve the
land texture...

-- 
┌─── dg@cowlark.com ─────
http://www.cowlark.com ─────
│
│ "I have a mind like a steel trap. It's rusty and full of dead mice."
│ --- Anonymous, on rasfc


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