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Incidentally, I bet snow would look fantastic with heavy SSS.

Hmm, something else to try. ;-)

- --
William Tracy
afi### [at] gmailcom -- wtr### [at] calpolyedu

You know you've been raytracing too long when you've ever thought or
said out-loud, "I'll bet I can raytrace that!"
    -- Neil Clark
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William Tracy <wtr### [at] calpolyedu> wrote:
> Trevor G Quayle wrote:
> > -maybe try different normal types: instead of granite or bumps,
>
> Take a peek at the code I posted farther up in the thread. Normals
> aren't really helpful here, because the surface is transparent. :-(
> Early on I tried normals on the solid surface *below* the SSS, but that
> made the patterns only visible on the dark side of the sand dunes, which
> is why my first screenshots were all backlit. :-)
>

Ah right, I see what you mean.  Forgot about the SSS.  Still, maybe try to use
the crackle or cell pattern for your density instead.

-tgq

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Some further thoughts on this.
Maybe you can still use normals, but try adding fresnel (or variable)
reflection.

Have a look at this photo: http://www.benzor.com/misc/desert.jpg

Part of the colouring and look of the sand appears to come from actual specular
reflection.

-tgq

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"Trevor G Quayle" <Tin### [at] hotmailcom> schreef in bericht 
news:web.47470378ee83a16cc150d4c10@news.povray.org...
> Looking pretty good.  Sand can be a difficult thing to simulate.  God idea
> trying some SSS with it.
>
> A few things you can try too.
> -as stated before, maybe don't use a uniform colour, but have a patterned
> varition as real sand tends to be
> -maybe try different normal types: instead of granite or bumps, you may 
> get
> better result using either a solid crackle, or cells pattern.  This will 
> give
> you flat surfaces with varying normals, and sharp transitions betwen 
> rather
> than the continuous transitions of other types.  You can also colour (or
> texture) map in cordination with the pattern used.  You may need good AA 
> though
> to get nice results.
>
> keep up the good work.
>


With the example William provided above, the cells pattern gives an 
excellent result!

Thomas

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"Thomas de Groot" <t.d### [at] internlDOTnet> schreef in bericht 
news:4747ebe9$1@news.povray.org...
>
> With the example William provided above, the cells pattern gives an 
> excellent result!

I forgot to say that I changed the scale to 0.0005 too, but that may vary 
with the scene involved.
Good work William!

Thomas

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Thomas de Groot wrote:
> Another possibility, I guess, would be to use the boxed or the cylindrical 
> patterns. Maybe cylindrical would be better than spherical in a landscape? 
> What do you think?

I just finished picking apart the code for "Picnic at Giza":
http://www.irtc.org/ftp/pub/stills/2004-08-31/em_giza.jpg

emkaah uses the following heightfield for the sand:
#declare PF0 = pigment{
  bumps
  turbulence 0.1
  color_map { [0 rgb .12] [1 rgb .1] } scale <1,.9,1>*0.1 translate x*-5
}
#declare PF1 = pigment{
  crackle
  form<.86,0,0>
  turbulence 0.4
  color_map { [0 rgb .105] [1 rgb .08] }
  scale <1,.8,10>*0.1
  translate <-2,-1,0>
}
#declare PF2 = pigment{
  bumps
  color_map { [0 rgb .11] [1 rgb .072] }
  scale .2
  translate x*-1
}
#declare PF=function {
  pigment{
    gradient z
    pigment_map{
      [0 PF0]
      [.40 PF0]
      [.50 PF1]
      [.60 PF2]
      [1 PF2]
    }
    turbulence .3
  }
}
#declare sandh1 = height_field{function 600,600 {PF(x,0,y).grey} /* lots
of extraneous parameters removed */ }

So, there's a gradient used as a pattern map, with PF0 being the pattern
in the foreground, PF1 in the midground, and PF2 in the distance.
There's some turbulence to keep the transitions from being too sharp.

PF2 is the pattern for the slope up just before the base of the
pyramids. It's a crackle pattern; that's how he got those neat little
valleys running down the slope.

I also want to fiddle with the source for "Mirage", from the same IRTC
round:
http://www.irtc.org/ftp/pub/stills/2004-08-31/mirage.jpg

What struck me about that image is that there's no doubt that the sand
in the image is *sand*. That's more than you can say for a lot of the
entries in that round. :-P

It's very stylized, but still instantly recognizable as sand.

- --
William Tracy
afi### [at] gmailcom -- wtr### [at] calpolyedu


> >  - Type 0 are tesselated dynamically during render time and the
> > tesselation results are discarded immediately once the intersections
> > are found. In particular, I noticed that POV accessed the u_order
> > and v_order variables and repetitively called the DeCasteljau
> > subdivision functions during intersection computations...

I see.

    -- Warp
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Thomas de Groot wrote:
> I forgot to say that I changed the scale to 0.0005 too, but that may vary 
> with the scene involved.
> Good work William!

Well thank-you. :-)

I've started playing with phong highlighting on the upper surface
coupled with noisy normals, though I don't really have anything to show yet.

It seems to me that phong or specular highlights are going to be much
more helpful than reflections.

- --
William Tracy
afi### [at] gmailcom -- wtr### [at] calpolyedu

You know you've been raytracing too long when you have archived more
than thousand rendered frames of an animation onto a CD to avoid ever
having to re-render.
    -- Aaron Gage a.k.a Slartibartfast
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"Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> "Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> schreef in bericht
> news:web.4746b46aee83a16ce8ba46670@news.povray.org...
>
> > I used a kind of 'fadeaway' technique for my snow texture for TerraPOV,
> > and I
> > posted recently and test render here. It is based on the distance wrt
> > camera
> > (use of spherical pattern): when near it is one texture, when far it tends
> > to
> > be a plain color (or whatever else). I intend to integrate fadeaway
> > texturing
> > macros like this in TerraPOV, because terrain pigments become plain colors
> > with
> > distance. Something like this can be applied to sand (same problem). It
> > can also
> > be used for other purposes, of course.
> >
>
> Another possibility, I guess, would be to use the boxed or the cylindrical
> patterns. Maybe cylindrical would be better than spherical in a landscape?
> What do you think?
>
> Thomas

Spherical and cylindrical patterns are equivalent when the camera is near the
ground. But if the camera is positionned high, only spherical is correct to
make things depend on distance.

    Bruno

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"Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> schreef in bericht 
news:web.474a77e7ee83a16ce8ba46670@news.povray.org...
> "Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
>> Another possibility, I guess, would be to use the boxed or the 
>> cylindrical
>> patterns. Maybe cylindrical would be better than spherical in a 
>> landscape?
>> What do you think?
>>
>> Thomas
>
> Spherical and cylindrical patterns are equivalent when the camera is near 
> the
> ground. But if the camera is positionned high, only spherical is correct 
> to
> make things depend on distance.
>
>    Bruno
>

Yes, that makes sense indeed. Thanks Bruno.

Thomas

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that looks pretty darn good.

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