On 6/16/2017 7:57 AM, Ari wrote:
> By the way, the thread URL is
>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.4d97bab0dc7be259e5cacc00%40news.povray.org%3E/?mtop=360023


I read the thread and if I understood it*. Sam used an external program, 
he developed himself, to calculate the positions of the grains.
So, in my opinion, unless using a third party program like bullet 
physics or Blender is acceptable. Then it would be very difficult to get 
the quality of Sam's image. But since you are a first year engineering 
student. It might be acceptable to use tools in addition to PovRay.

*

I am no mathematician.

It raises an interesting philosophical question.

Were you given that image and told to reproduce it or did you pick it 
yourself?
Does the person who gave you the problem have a solution?
And in an engineering frame. What tolerances do you need to work to?


I said that I was no mathematician and that is two questions. ;-)



-- 

Regards
     Stephen

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Stephen <mca### [at] aolcom> wrote:
> On 6/16/2017 7:57 AM, Ari wrote:
> > By the way, the thread URL is
> >
http://news.povray.org/povray.binaries.images/thread/%3Cweb.4d97bab0dc7be259e5cacc00%40news.povray.org%3E/?mtop=360
023
>
> I read the thread and if I understood it*. Sam used an external program,
> he developed himself, to calculate the positions of the grains.

A wizard for sure, as are many others. I missed so much all those years ago but
already had seen plenty being done by Samuel.

I guess if I were to attempt my own "stacking stones" it would probably be
something like I had used for object interactions with simplistic 'sphere of
influence' for mass and gravity when I was doing rudimentary space simulations
in Basic programming (circa 1980's).
Not ideal for this, even if I could get it right in POV-Ray.

Bob

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On 6/16/2017 10:18 AM, omniverse wrote:
> Stephen <mca### [at] aolcom> wrote:
>> On 6/16/2017 7:57 AM, Ari wrote:
>>> By the way, the thread URL is
>>>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.4d97bab0dc7be259e5cacc00%40news.povray.org%3E/?mtop=360
> 023
>>
>> I read the thread and if I understood it*. Sam used an external program,
>> he developed himself, to calculate the positions of the grains.
>
> A wizard for sure, as are many others. I missed so much all those years ago but
> already had seen plenty being done by Samuel.
>

Yes a wizard. I wonder when he will reappear to drop off another gem.

> I guess if I were to attempt my own "stacking stones" it would probably be
> something like I had used for object interactions with simplistic 'sphere of
> influence' for mass and gravity when I was doing rudimentary space simulations
> in Basic programming (circa 1980's).

Ah! basic. Now you are talking. :)
I managed to get a lander program working on a Casio calculator, in basic.

> Not ideal for this, even if I could get it right in POV-Ray.
>


I can see it working on rectangular stones as in a dry stone dyke. You 
would not have to be too concerned about gaps between rounded stones, I 
think.


-- 

Regards
     Stephen

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"Ari" <win### [at] yahoocomhk> wrote:

> By the way, the thread URL is
>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.4d97bab0dc7be259e5cacc00%40news.povray.org%3E/?mtop=36002
3


Aha.
That was a good read, and I'd say that some excellent info is contained therein
- especially the scene code and that last post.

Up to this point, I'd say that the focus has been on using a random placement as
the fundamental method by which to build the pile, however, a stepwise #while
loop that built the pile up in strata would be a different approach - with
different advantages and challenges.

I'd say that there's a whole world of interesting algorithmic material out there
that could be applied to this, and certainly the Graphics Gems series and some
of those Numerical Recipes type code examples might help.
You might want to take a look at things like Appolonian Gaskets, Steiner circles
and spheres, canal and channel surfaces, fractals, closest packing schemes and
crystallography, and Voronoi diagrams and Delaunay triangulations.

http://paulbourke.net/fractals/apollony/


The key at this point though, is to keep it simple and fast enough to get the
job done.  Don't "let the perfect be the enemy of the good." ;)

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Stephen <mca### [at] aolcom> wrote:
> .... Sam used an external program,
> he developed himself, to calculate the positions of the grains.

I'd say that he probably used Voroi++
http://math.lbl.gov/voro++/examples/

which from the download page, says that the output can be used in POV-Ray
http://math.lbl.gov/voro++/download/

What would be nice would be a way to shell out to Voroi++ to generate the data
for a scene and then render it.

I just don't know how to do that ([like many things] yet).

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On 6/16/2017 6:10 PM, Bald Eagle wrote:
> Stephen <mca### [at] aolcom> wrote:
>> .... Sam used an external program,
>> he developed himself, to calculate the positions of the grains.
>
> I'd say that he probably used Voroi++
> http://math.lbl.gov/voro++/examples/
>
> which from the download page, says that the output can be used in POV-Ray
> http://math.lbl.gov/voro++/download/
>
> What would be nice would be a way to shell out to Voroi++ to generate the data
> for a scene and then render it.
>
> I just don't know how to do that ([like many things] yet).
>
>
It is not really that difficult. At least it wasn't in Ver 3.5. When I 
last used the function. You write a text file in PovRay with the 
variables you need and get the 3rd party software to export the results 
of the calculations to a text file that PovRay can read.
Yes this would be an animation even if it is only two frames or a frame 
per layer.

I ask myself if something this complex is appropriate for a first year 
engineering course.  But then my first year at university detailed 
thermionic valves and ne'er a mention of semiconductors. :) So things 
might have changed.

-- 

Regards
     Stephen

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Stephen <mca### [at] aolcom> wrote:

> It is not really that difficult. At least it wasn't in Ver 3.5. When I
> last used the function. You write a text file in PovRay with the
> variables you need and get the 3rd party software to export the results
> of the calculations to a text file that PovRay can read.
> Yes this would be an animation even if it is only two frames or a frame
> per layer.

I guess my question was whether or not Voro++ is set up to accept comman-line
parameters and return a file for immediate processing by POV-Ray.
If so, then it would be of great interest to those who have a continuing
interest in having direct access to the set of coordinates used for the crackle
pattern - by supplanting crackle with a Voro++ data file, that would be a great
workaround.

> I ask myself if something this complex is appropriate for a first year
> engineering course.  But then my first year at university detailed
> thermionic valves and ne'er a mention of semiconductors. :) So things
> might have changed.

It ought to be perfectly fine.
I remember the engineers on my floor constantly being immersed in Statics:

http://ruina.tam.cornell.edu/Book/RuinaPratap8-21-10.pdf

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Am 2017-06-16 03:35, also sprach Stephen:

> I read the thread and if I understood it*. Sam used an external program, 
> he developed himself, to calculate the positions of the grains.

I, too, use a Java program to position grains. I found SDL to be 
hideously slow when doing a 1600 x 1600 loop. ;)
http://www.buckosoft.com/tteoac/video/frames/ttfo0177.png

I love Sam's idea; pick a position and then alter the blob's shape and 
size to fit the position.


-- 
dik

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Omg, Guys!
I just cannot believe how generous and warm this community is.
I am sorry that I just completely immersed myself in this software (I only got 2
months to learn this technique :( And it is making me anxious now) therefore I
cannot check this thread frequently. Thanks again for the big help! Even though
I cannot reply the messages one by one, I swear I would read all the useful
information I have received. Again, I just cannot how generous this community
could be at the first glance. A big shoutout to all of you :D.

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On 6/17/2017 9:02 AM, Ari wrote:
> Omg, Guys!
> I just cannot believe how generous and warm this community is.

Oh! you have not received the invoice, yet. :)

-- 

Regards
     Stephen

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