On 21-6-2017 13:58, Bald Eagle wrote:
> 
> Without really knowing exactly what I was doing, and just plugging some stuff
> into the editor and changing some values, I got this in 5 min:
> (many thanks to Mike Williams   http://www.econym.demon.co.uk/isotut/
> and David Wagner   http://wiki.waggy.org/dokuwiki/povray/stainedglass)
> 
> #version 3.71;
> 
> global_settings {
>    assumed_gamma 1.0
> }
> 
> #include "colors.inc"
> 
> camera {
>   location  <0.0, 0, -5.0>
>   right    x*image_width/image_height
>   look_at   <0, 0, 0>}
> 
> light_source {<10, 10, -30> White}
> 
> #declare Packing = 1.3; //(increase to make more tightly packed)
> 
> #declare F =
> function {
>   pigment {
>    crackle
>    form < -1, Packing, 0>
>    metric 3
>    offset 0
>    turbulence 0.1
>    color_map { [0 rgb 1] [0.99 rgb 0] [1 rgb 0] }
>    scale 0.25
>   }
> }
> 
> isosurface {
>          function { F(x,y,z).red - 0.5 }
>          max_gradient 5.5
>          contained_by{box{-1,1}}
>          pigment {rgb 0.9}
> }
> 
> Just needs some tweaking, colors and textures.
> NO idea how to get the parts sliced smooth by the container removed, but I
> supposed doing a difference or intersection with a highly textured box or
> something might be a good way to fake it.
> 

This is a nice try but... it is not a /stacking/ of stones. It is a 
crackled volume. If you drop stones, they will behave differently from 
what you see here.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:

> This is a nice try but... it is not a /stacking/ of stones. It is a
> crackled volume. If you drop stones, they will behave differently from
> what you see here.

Indeed - it wasn't really even supposed to be a "try" - it was just a blatant
cut&paste with a minor tweak or two to get it to run and close up the gaps a bit
- to show that with a wee bit of POV-Ray magic, a 3-dimensional Voronoi diagram
that gives the appearance of a pile of "stones" is THAT quick and easy - no
math, no (user-written) algorithms, no staying up late, pulling out one's
(remaining) hair, no crying in the corner because you're stoopid.

And to pick nits, if you drop stones, they will of course [sic] behave
differently than if you stack them.

AND the end result is going to be a product of however the user codes the scene
anyway, will will be a further layer of deviation from reality.

I'd say we're at a juncture where the parameters of the project need to be
defined.  But there still all sorts of fun variations on the theme that we can
play with - unconstrained by the prof.   :)
(which is what the _really_ good students ought to be doing along the way / in
addition to the stated project)

"So, I made that rock pile that you wanted - but I also did a few old Scottish
castles, the Great Wall of China, a cross-section of an archaeological
excavation site with some fossil meshes thrown in, an animated exploding Rice
Krispy treat, the rubble in the aftermath of a Kalifornia earthquake, and I've
begun a study on the kinetics of settling in a mixture of sand, aggregate, and
cement in pre-mixed concrete....... by the way is there any more coffee?"
;)

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"Bald Eagle" <cre### [at] netscapenet> wrote:
> Without really knowing exactly what I was doing, and just plugging some stuff
> into the editor and changing some values, I got this in 5 min:
> [code example]

Cool. I've been playing with it and animating some of the values, to see what
happens. Fun!

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Le 17-06-21 à 07:58, Bald Eagle a écrit :
> 
> Without really knowing exactly what I was doing, and just plugging some stuff
> into the editor and changing some values, I got this in 5 min:
> (many thanks to Mike Williams   http://www.econym.demon.co.uk/isotut/
> and David Wagner   http://wiki.waggy.org/dokuwiki/povray/stainedglass)
> 
> #version 3.71;
> 
> global_settings {
>    assumed_gamma 1.0
> }
> 
> #include "colors.inc"
> 
> camera {
>   location  <0.0, 0, -5.0>
>   right    x*image_width/image_height
>   look_at   <0, 0, 0>}
> 
> light_source {<10, 10, -30> White}
> 
> #declare Packing = 1.3; //(increase to make more tightly packed)
> 
> #declare F =
> function {
>   pigment {
>    crackle
>    form < -1, Packing, 0>
>    metric 3
>    offset 0
>    turbulence 0.1
>    color_map { [0 rgb 1] [0.99 rgb 0] [1 rgb 0] }
>    scale 0.25
>   }
> }
> 
> isosurface {
>          function { F(x,y,z).red - 0.5 }
>          max_gradient 5.5
>          contained_by{box{-1,1}}
>          pigment {rgb 0.9}
> }
> 
> Just needs some tweaking, colors and textures.
> NO idea how to get the parts sliced smooth by the container removed, but I
> supposed doing a difference or intersection with a highly textured box or
> something might be a good way to fake it.
> 
> Sorry officer, there was no posted speed limit.
> 
> 
> 

You can use multiple patterns. In this case, a boxed pattern may be 
usefull with a colour_map that stays to 1 untill close to the edges, 
then drops to zero over a relatively short distance. Something like this:

#declare F_Boxed = function{colour_map{[0 rgb 0][0.1 rgb 1]}}

Next, you multiply the two.
isosurface {
         function { F(x,y,z).red - 0.5 } * function{F_Boxed(x,y,z).red}
         max_gradient 5.5
         contained_by{box{-1,1}}
         pigment {rgb 0.9}
}

Post a reply to this message

On 22-6-2017 13:50, Bald Eagle wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>> This is a nice try but... it is not a /stacking/ of stones. It is a
>> crackled volume. If you drop stones, they will behave differently from
>> what you see here.
> 
> Indeed - it wasn't really even supposed to be a "try" - it was just a blatant
> cut&paste with a minor tweak or two to get it to run and close up the gaps a bit
> - to show that with a wee bit of POV-Ray magic, a 3-dimensional Voronoi diagram
> that gives the appearance of a pile of "stones" is THAT quick and easy - no
> math, no (user-written) algorithms, no staying up late, pulling out one's
> (remaining) hair, no crying in the corner because you're stoopid.
> 
> And to pick nits, if you drop stones, they will of course [sic] behave
> differently than if you stack them.
> 
> AND the end result is going to be a product of however the user codes the scene
> anyway, will will be a further layer of deviation from reality.
> 
> I'd say we're at a juncture where the parameters of the project need to be
> defined.  But there still all sorts of fun variations on the theme that we can
> play with - unconstrained by the prof.   :)
> (which is what the _really_ good students ought to be doing along the way / in
> addition to the stated project)
> 
> "So, I made that rock pile that you wanted - but I also did a few old Scottish
> castles, the Great Wall of China, a cross-section of an archaeological
> excavation site with some fossil meshes thrown in, an animated exploding Rice
> Krispy treat, the rubble in the aftermath of a Kalifornia earthquake, and I've
> begun a study on the kinetics of settling in a mixture of sand, aggregate, and
> cement in pre-mixed concrete....... by the way is there any more coffee?"
> ;)
> 
> 

I can only agree with you :-)

To tell the truth, I was not criticising your crackle which is fine by 
itself and useful in other contexts (a mortared wall?) I wanted to draw 
attention (mine included) to the very different geometry presented by 
stacking stones. Obvious, and yet something to ponder deeply for 
modelling purposes. :-)

-- 
Thomas

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On 6/23/2017 7:37 AM, Thomas de Groot wrote:
> To tell the truth, I was not criticising your crackle which is fine by
> itself and useful in other contexts (a mortared wall?) I wanted to draw
> attention (mine included) to the very different geometry presented by
> stacking stones. Obvious, and yet something to ponder deeply for
> modelling purposes. :-)

I've spent two days making rocks and trying to lay them in a single 
layer. I'm really struggling with it.

-- 

Regards
     Stephen

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On 23-6-2017 12:09, Stephen wrote:
> On 6/23/2017 7:37 AM, Thomas de Groot wrote:
>> To tell the truth, I was not criticising your crackle which is fine by
>> itself and useful in other contexts (a mortared wall?) I wanted to draw
>> attention (mine included) to the very different geometry presented by
>> stacking stones. Obvious, and yet something to ponder deeply for
>> modelling purposes. :-)
> 
> I've spent two days making rocks and trying to lay them in a single 
> layer. I'm really struggling with it.
> 

Yes it is a very difficult task, especially considering how easily 
Mother Nature does it herself. ;-)

Steering clear from specialised modelling packages which can do this, 
and trying to restrict myself to only POV-Ray, trace() is an obvious 
tool but it needs to be completed with some kind of gravity (vertical; 
trace -y) and/or stream energy (horizontal; trace +/-x or +/-z) control 
to settle individual grains before, during, and after impacts over a 
number of incrementing iterations. Not easy!

-- 
Thomas

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On 23-6-2017 13:21, Thomas de Groot wrote:
> Steering clear from specialised modelling packages which can do this, 
> and trying to restrict myself to only POV-Ray, trace() is an obvious 
> tool but it needs to be completed with some kind of gravity (vertical; 
> trace -y) and/or stream energy (horizontal; trace +/-x or +/-z) control 
> to settle individual grains before, during, and after impacts over a 
> number of incrementing iterations. Not easy!
> 

Something like this would be nice :-o

https://www.deltares.nl/academy/delft3d-4-modelling-sediment-transport-and-bed-dynamics/

-- 
Thomas

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I will just say that there apparently has been much work done on exactly this.

Makes for some very interesting reading.

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On 23-6-2017 21:19, Bald Eagle wrote:
> 
> I will just say that there apparently has been much work done on exactly this.
> 
> Makes for some very interesting reading.
> 
> 

Coastal engineering in the Netherlands has a worldwide reputation. 
However, I do not think that they model/stack the sand grains 
individually like we would like to do, and in fact that is far less 
interesting for their purpose. What they model are the different scale 
sediment transport mechanisms under variable space/time/sediment 
availability/composition conditions.

-- 
Thomas

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