POV-Ray : Newsgroups : povray.binaries.images : SSLT with the Granite_21_beta1.7 macro : Re: SSLT with the Granite_21_beta1.7 macro Server Time
2 Aug 2021 03:10:06 EDT (-0400)
  Re: SSLT with the Granite_21_beta1.7 macro  
From: Thomas de Groot
Date: 4 Jul 2021 07:52:09
Message: <60e1a0e9$1@news.povray.org>
Op 4-7-2021 om 10:41 schreef Dave Blandston:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> A granite would not look like this. This is more like a granite-textured
>> kind of pottery. What is missing is the internal structure of minerals,
>> especially in the ears. I am pondering the problem and think into the
>> direction of a media, or maybe, a special kind of isosurface (I am
>> thinking of my rings of Saturn in 2017), or again, a rand_in_object fill
>> with small particles.
> 
> 
> Wow this looks extremely promising. I think you are on the verge of a major
> accomplishment!
> 
He he! We are getting there, slowly indeed. ;-)

> I visited a local granite supply store again recently to look more carefully at
> real granite. If I may make a humble suggestion relative to the current phase of
> your project based on what I saw it would be this: The samples that I observed
> that demonstrated SSLT only seemed to have SSLT properties in the veins, or
> perhaps certain types of crystals but not others. The same was true of the
> "sparkly" and/or iridescent elements. Perchance that condition was unique to the
> granite samples that the business happened to have in stock at that time. I have
> no idea whether or not a larger set of samples would reveal that that is a
> universal rule >
Yes, you are absolutely right. The point is indeed that only some of the 
minerals composing the rocks are transparent/-lucent. Quartz and 
calcite, which form most of the veins, but also some of the more 
colourful minerals of the plagioclase class (the pink or grey ones). 
Others are perfectly opaque. So, getting this in a (3D) sslt scheme is a 
challenge indeed. I have been experimenting with additional filter 
values in the vein's colour maps but that is difficult and highly 
controversial at the moment.

The 'larvikite' which you showed in another post, the one with those 
iridescent minerals, is a special case of 'monzonite' 
https://en.wikipedia.org/wiki/Larvikite . It resides at the fringe of 
the granite field. It would be a challenge in its own right of course. 
Sam Benge has done some perfect modelling of jaspers which would come 
close, but I would prefer to concentrate on the 'classic' granites which 
are already given enough trouble by themselves ;-).

I can tell that, at the moment, I have five different granites ready, 
based on Daniel Mecklenburg's original colour maps: Dakota Red, North 

In due time, I shall post them. My philosophy at the moment is that - as 
those originals are commercial names and products, possibly not even 
'real' granites but also gneisses or other metamorphic rocks - I 
transform them to my own understanding into my own 'real' granites, 
keeping the name, but differing quite possibly from the original stuff. 
With a little utility provided by Bald Eagle, this has been made much 
easier now and will be made much easier also for the users themselves 
who want to design their own granites (which is all the fun of course).

> Also, I noticed that some granite is like the Dakota Red as far as scale, for
> example a 1" x 1" piece is all you need in order to know what the pattern looks
> like. There were some samples with a much larger scale (although the individual
> crystals were probably similar in size) and by that I mean that you would need a
> much larger piece in order to get an idea of what the pattern looked like. In
> some cases a 3- or 4-square-foot or even larger piece would be necessary.
> 
Yes. I /think/ that the user will be able to play with those pattern 
changes and pattern scales, using the provided pigment_pattern mask 
arrays, and variations arrays. They are very powerful and subtle means 
to model the granite one wants. In fact, each granite can be modelled 
into almost an infinity of different variations with only very little 
changes to the arrays. I need to expand part of the future documentation 
to cover this particularly fascinating aspect of the macro.

I am not finished to be surprised by my own macro indeed. ;-)

> I promise I'm not trying to complicate your project, I'm just mentioning what I
> saw.
> 
And rightfully thanked you are. These comments help to hone my own 
understanding of the whole process indeed.

-- 
Thomas


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