I took your sample and source, played with it, and modified it.  Please take
a look to see if this will help you...

Will post the sources in the response to this post.

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Attachments:
Download 'capture_07132006_153301.png' (157 KB)

Preview of image 'capture_07132006_153301.png'

Included is the crater image used for this render.  Below is the modified
source.

// Asteroid
#version 3.6;
// ==============================================================
#default{finish{ambient 0}}
#global_settings{assumed_gamma 1.0 max_trace_level 5}

#declare f_bozo1 = // similar to noise3d
function{pigment{bozo scale 0.5 color_map{[0 color rgb 0] [1 color rgb 1]}}}

#declare f_craters =
function{
/*  pigment{
    crackle form <1.2, 0, 0> // never really played with this one, thaks
Yadgar!
    scale 0.3
    color_map{
      [0.00 color rgb 1.00] // centre of crater, lowest part
      [0.30 color rgb 0.80] //
      [0.35 color rgb 0.40] // rim, higher than surrounding area
      [0.40 color rgb 0.5] // level of area outside the crater
      [1.00 color rgb 0.5]
    }
  }*/
  pigment{
 image_map{
   png "crater-image.png"
   map_type 1
   interpolate 2
  }
 }

}

/*
the f_craters function is subtracted from the basic asteroid shape, so the
lowest points get the highest numbers, since you are subtracting more.
*/

// --------------------------------------------------------------
isosurface{
  function{
    (x*x)+(y*y*1.8)+(z*z*1.5)-1 // basic sphere function, scaled to be more
                                // elliptical
    +f_bozo1(x,y,z).red*0.35 // deforms the ellipse shape
    +f_craters(x,y,z).red*0.5 // adjust the '*0.05' part to change the depth
of
                              //the craters
  }
  contained_by{box{<-1, -1, -1>, <1, 1, 1>}}
  threshold 0
  accuracy 0.001
  #local _grad_value=48.13;
// max_gradient _grad_value
  #local _P1=_grad_value*0.6;
  #local _P2=sqrt(_grad_value/_P1);
  #local _P3=0.7;
  evaluate _P1, _P2, _P3

  texture{
   pigment{
    color rgb 1
   }
   finish{
    diffuse 0.6
    ambient color rgb<0.2, 0.4, 1.0>*0.0625
   }
  }
}

light_source{<-10, 10, -5> color rgb 1}
//light_source{< 10, -10, -5> color rgb<0.2, 0.4, 1.0>*0.25}

camera{
  location <0, 1, -4>
  up y*(image_height/image_width)
  right x
  sky y
  look_at <0, 0, 0>
  angle 36
}

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Attachments:
Download 'crater-image.png' (252 KB)

Preview of image 'crater-image.png'

Physics-wise, there seems to be ambient light in the image. Where
would this light be coming from?-)

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Warp <war### [at] tagpovrayorg> wrote:
> Physics-wise, there seems to be ambient light in the image. Where
> would this light be coming from?-)

You're right, I was experimenting with the ambient parameter in the object.

I think it might be better to just have a second light source to lighten up
the dark side.

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High!

EagleSun wrote:
> I took your sample and source, played with it, and modified it.  Please take
> a look to see if this will help you...
> 
> Will post the sources in the response to this post.

Not very convincing... most asteroids are darker, and their crater rims 
aren't as pronounced as on your picture, instead, they are more or less 
subdued by erosion because of billions and billions of micro-impacts. 
And at least the large crater facing the camera is elongated - which 
almost never happens in reality!

Here is what I put together after Mark's last posting (still WIP)... 
note the scale bars included!

My asteroid is far from being finished, as I noted two strange effects: 
firstly, even though I provided also a few larger craters in my 
13-partite combined crater function, after averaging it with small-scale 
noise (for simulating micro-impact erosion), these larger ones 
disappeared completely, and secondly, when I use a crater function 
consisting of more then 13 individual crater "layers" (i. e. single 
crackle <x, 0, 0> functions), no craters are rendered at all!

In the future, I also plan to add several 10,000 random boulders to be 
placed on the surface of the asteroid, a view from "pedestrian 
perspective", perhaps even a surface sampling probe just landed (like 
Japanese-made Hayabusa)...

See you in Khyberspace!

Yadgar

Now playing: Sayonara ('til we meet again) (Taco)

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Attachments:
Download '2006-07-09 michatopia, moon .jpg' (75 KB) Download '2006-07-10 michatopia, moon .jpg' (70 KB) Download '2006-07-10 michatopia, moon .jpg' (77 KB) Download '2006-07-10 michatopia, moon .jpg' (70 KB) Download '2006-07-10 michatopia, moon .jpg' (73 KB) Download '2006-07-10 michatopia, moon .jpg' (70 KB) Download '2006-07-11 michatopia, moon .jpg' (77 KB) Download '2006-07-11 michatopia, moon .jpg' (80 KB) Download '2006-07-12 michatopia, moon .jpg' (86 KB)

Preview of image '2006-07-09 michatopia, moon .jpg'

Preview of image '2006-07-10 michatopia, moon .jpg'

Preview of image '2006-07-10 michatopia, moon .jpg'

Preview of image '2006-07-10 michatopia, moon .jpg'

Preview of image '2006-07-10 michatopia, moon .jpg'

Preview of image '2006-07-10 michatopia, moon .jpg'

Preview of image '2006-07-11 michatopia, moon .jpg'

Preview of image '2006-07-11 michatopia, moon .jpg'

Preview of image '2006-07-12 michatopia, moon .jpg'

Where did you get the crater map from?
Is it procedural or from something like DEM data?

The planar image map doesn't really work well mapped onto a sphere, but I
tried rendering it as a height field and it looks great!

If it is a DEM type map then it's still great reference for trying to figure
out a procedural imitaion of it.

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EagleSun wrote:
> I think it might be better to just have a second light source to lighten up
> the dark side.

   Wouldn't that be kind of awkward in space? Unless there would be
some other object (eg. another, possibly bigger, asteroid) reflecting
sunlight on the other side?-)

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Great, natural looking asteroid! Hmm... But the color indicates chalk or 
ice, while the structure indicates real stone. The color should be the color 
of stone, as well. But it is a wow-asteroid, already!!!

Best greetings,

Sven

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"Sven Littkowski" <sve### [at] jamaica-focuscom> wrote:
> Great, natural looking asteroid! Hmm... But the color indicates chalk or
> ice, while the structure indicates real stone. The color should be the color
> of stone, as well. But it is a wow-asteroid, already!!!
>
> Best greetings,
>
> Sven

Hi Group!

The crater map was obtained from somewhere... (sorry for being vague on this
because I don't remember where exactly...) and my limited memory thinks it
might have been related to a site having information about the moon.  After
rendering, I'm OK with it if you make the claim that this crater map was
generated by computer.  The original crater map is 4000 x 4000, 16-bit,
where white represents high altitude and black represents low altitude.  I
had to reduce the size, and I inverted it because the iso-surface function
has backwards interpretation.

I was playing around with ambient parameter.  In a realistic situation, I
would shut down that parameter completely.  And I wouldn't make a second
light source either.  But there has been recent posts where the second
light source was included, so I thought to kinda maintain it for a while.
Now come to think of it... many of the asteroids are kinda close to
Jupiter.  Could there be an orangish second light source?

I only did a practice in hope it would be helpful for someone to pick it up
and perfect it.  Later I realized someone had developed a really nice
crater and erosion functions.

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