Op 27-10-2021 om 11:44 schreef MichaelJF:
> IIRC you're using Silo, but I have no idea if Silo can handle this kind 
> of plane intersections. Blender can load the WRL data. But as I noticed 
> these intersecting planes I wondered about the photons. Usually infinite 
> objects are not recommended as photon targets.
> 
Correct. I use Silo, which is why I mentioned an .obj version of the wrl 
data by Poseray. Silo does not accept wrl data.

In the meantime, I have done a mesh2 version of the wrl data through 
Poseray and that works fine. I had forgotten about the possible trouble 
of infinite objects when using photons, so I shall use the mesh2 
exclusively with them. Thanks for the reminder indeed.

-- 
Thomas

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Crystal replaced by a mesh2 version. Less grainy by not using 
stochastic. Render time about 27 minutes. Collected photons, about 1 GB.

Additional scene developments pending.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> Crystal replaced by a mesh2 version. Less grainy by not using
> stochastic. Render time about 27 minutes. Collected photons, about 1 GB.
>
> Additional scene developments pending.

It's looking better and a little less noisy now. It also seems a bit more
bluish. Looking online, this mineral has a range of hues spanning between
colorless, pale yellow, and pale/bluish green. All seem to be valid.

>> How long did this take to render? The file name says 004d, so I really hope it
>> wasn't 4 days ':/
>
> Oh no! That is the version number ;-) This render was pretty fast: less
> than an hour iirc.

Thank goodness, lol. That makes more sense.

>> I'd like to discover a cheap and realistic way to add internal fractures to
>> mineral renders. Apophyllite is one of those minerals prone to being found in a
>> fractured state. I have two ideas in mind, but both are rather expensive: 1)
>> height fields intersecting not only each other, but also the crystal shape
>> (which is itself an intersection); or 2) isosurfaces. Both can be very, very
>> slow. Sometimes I wish media had an ior block.
>
> Ah... yes indeed. I have not considered your first method, but
> considered the isosurface one. However, I also cringe at the implied
> render time.

Both methods are going to be slow, yeah. And care must be taken when choosing
the fracture planes for a given mineral. Apophyllite appears to exhibit basal
cleavage, so its fractures tend to be horizontal more often than not.

And then there are clouds... Similar to fractures, the clouds you see in
minerals are often reflective/refractive gas or liquid pockets, and so they
might not easily be replicated with scattering media. (It seems to me that there
was an experimental version of POV-Ray a long time ago which allowed one to
specify the reflectivity of participating media. I wonder what happened to
that?)

> Another thing I would like to do is model more asymmetric crystals, like
> they occur in nature. The KrystalShaper models are too perfect for our
> grubby little hands. :-) Maybe by carefully manipulating the set of
> planes in the intersection, or working directly on a mesh2 model
> converted back to .obj for instance, and load it up in our favourite
> modeller...

Personally, before going that far, I'd just change the distance values of each
crystal face in KrystalShaper, and not even mess with any other program save
POV-Ray. KS is great like that; you can make entirely new minerals if you wish.
And there's always doing what I did: copy the HKL+distance data to POV-readable
arrays. Then you could take it a step further and add some randomization before
the HKL+D data is used to make the intersection.

Besides the symmetry, another thing I noticed about the crystal libraries in KS
is that the secondary and tertiary faces (modifications) tend to be somewhat
exaggerated. My alum render, for instance, was not what you'd consider a typical
specimen; you'd usually only see eight main faces in real life. And the
apophyllite model is the same way: in nature you usually only see cuboids
truncated with a steep pyramid. (The bevel between pyramid faces is atypical.)
None of this is a bad thing, of course, and it helps to show us just how a
mineral can form secondary & tertiary faces.

Sam

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Op 27/10/2021 om 22:44 schreef Samuel B.:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Crystal replaced by a mesh2 version. Less grainy by not using
>> stochastic. Render time about 27 minutes. Collected photons, about 1 GB.
>>
>> Additional scene developments pending.
> 
> It's looking better and a little less noisy now. It also seems a bit more
> bluish. Looking online, this mineral has a range of hues spanning between
> colorless, pale yellow, and pale/bluish green. All seem to be valid.
> 
Yes, in between renders I added a bit more blue.

>>> How long did this take to render? The file name says 004d, so I really hope it
>>> wasn't 4 days ':/
>>
>> Oh no! That is the version number ;-) This render was pretty fast: less
>> than an hour iirc.
> 
> Thank goodness, lol. That makes more sense.
> 
Yes, it is rather fast.

In my latest experiment, I cranked photon spacing down to 0.001 (for the 
examples shown here, this was 0.004) but then POV-Ray stopped along the 
parsing way, with an 'out of memory' message. Even 0.004 might be 
overkill for all I know; I shall need to investigate.

>>> I'd like to discover a cheap and realistic way to add internal fractures to
>>> mineral renders. Apophyllite is one of those minerals prone to being found in a
>>> fractured state. I have two ideas in mind, but both are rather expensive: 1)
>>> height fields intersecting not only each other, but also the crystal shape
>>> (which is itself an intersection); or 2) isosurfaces. Both can be very, very
>>> slow. Sometimes I wish media had an ior block.
>>
>> Ah... yes indeed. I have not considered your first method, but
>> considered the isosurface one. However, I also cringe at the implied
>> render time.
> 
> Both methods are going to be slow, yeah. And care must be taken when choosing
> the fracture planes for a given mineral. Apophyllite appears to exhibit basal
> cleavage, so its fractures tend to be horizontal more often than not.
> 
Correct. This needs a good knowledge of crystallography indeed. I am a 
layman on this really...

> And then there are clouds... Similar to fractures, the clouds you see in
> minerals are often reflective/refractive gas or liquid pockets, and so they
> might not easily be replicated with scattering media. (It seems to me that there
> was an experimental version of POV-Ray a long time ago which allowed one to
> specify the reflectivity of participating media. I wonder what happened to
> that?)
> 
Inclusions, yes. Scattering media is a poor substitute. There are the 
little foreign grains that got included, and the fluid inclusions. Those 
are really interesting!

[Aside] in a very distant past, my wife did a study on fluid inclusions 
in quartz crystals from Greece. She could, by cooling the crystals in 
liquid nitrogen and then slow heating, determine the original 
temperature of the liquid in which the crystal grew. Original pressure 
was somehow derived from other factors. I forgot. [/Aside]

But, those fluid inclusions are difficult to model. I was thinking about 
clouds of bubbles in liquid (there are a couple of scene files drifting 
around in the pov world; I think I have a couple of those somewhere) 
using a gaussian distribution scheme...

>> Another thing I would like to do is model more asymmetric crystals, like
>> they occur in nature. The KrystalShaper models are too perfect for our
>> grubby little hands. :-) Maybe by carefully manipulating the set of
>> planes in the intersection, or working directly on a mesh2 model
>> converted back to .obj for instance, and load it up in our favourite
>> modeller...
> 
> Personally, before going that far, I'd just change the distance values of each
> crystal face in KrystalShaper, and not even mess with any other program save
> POV-Ray. KS is great like that; you can make entirely new minerals if you wish.
> And there's always doing what I did: copy the HKL+distance data to POV-readable
> arrays. Then you could take it a step further and add some randomization before
> the HKL+D data is used to make the intersection.
> 
Yes, I think you are right there.

> Besides the symmetry, another thing I noticed about the crystal libraries in KS
> is that the secondary and tertiary faces (modifications) tend to be somewhat
> exaggerated. My alum render, for instance, was not what you'd consider a typical
> specimen; you'd usually only see eight main faces in real life. And the
> apophyllite model is the same way: in nature you usually only see cuboids
> truncated with a steep pyramid. (The bevel between pyramid faces is atypical.)
> None of this is a bad thing, of course, and it helps to show us just how a
> mineral can form secondary & tertiary faces.
> 
Yes, I have been wondering about that. Not being an expert, I have been 
hesitating between the different models proposed.

-- 
Thomas

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Op 27-10-2021 om 22:44 schreef Samuel B.:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>>> How long did this take to render? The file name says 004d, so I really hope it
>>> wasn't 4 days ':/
>>
>> Oh no! That is the version number ;-) This render was pretty fast: less
>> than an hour iirc.
> 
> Thank goodness, lol. That makes more sense.
> 
Strange. Somehow, I must have changed something, but now renders take a 
much longer time, more in the range of several hours (and photons jumped 
to 3Gb). I do not remember what is different. :-/

-- 
Thomas

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Op 28-10-2021 om 16:38 schreef Thomas de Groot:
> Strange. Somehow, I must have changed something, but now renders take a 
> much longer time, more in the range of several hours (and photons jumped 
> to 3Gb). I do not remember what is different. :-/
> 
Found the culprit! :-)

I had changed 'union' to 'merge' in the mesh2 object. In this particular 
case of well-behaving crystal faces, that is unnecessary. The render 
speed difference is dramatic indeed.

-- 
Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> Op 27/10/2021 om 22:44 schreef Samuel B.:
> > Thomas de Groot <tho### [at] degrootorg> wrote:
> >> Ah... yes indeed. I have not considered your first method, but
> >> considered the isosurface one. However, I also cringe at the implied
> >> render time.
> >
> > (...) care must be taken when choosing the fracture planes for a given mineral
(...)
> >
> Correct. This needs a good knowledge of crystallography indeed. I am a
> layman on this really...

It doesn't really take any in-depth knowledge. Just a bit of time reading and
browsing through images of minerals. (Which might be too time-consuming,
depending...)

> > And then there are clouds... Similar to fractures, the clouds you see in
> > minerals are often reflective/refractive gas or liquid pockets, and so they
> > might not easily be replicated with scattering media. (...)
> >
> Inclusions, yes. Scattering media is a poor substitute. There are the
> little foreign grains that got included, and the fluid inclusions. Those
> are really interesting!

Yeah, there are many fascinating inclusions that can occur in minerals. I
remember seeing a photo of some white crystals occasionally found in obsidian.
IIRC, they formed in groups of four tetrahedral crystals meeting at their
corners. Pretty much like the first iteration of a Sierpinski tetrahedron. If I
come across the image again, I'll post it. (Image search isn't turning up
anything relevant, and I originally found it in a book.)

> [Aside] in a very distant past, my wife did a study on fluid inclusions
> in quartz crystals from Greece. She could, by cooling the crystals in
> liquid nitrogen and then slow heating, determine the original
> temperature of the liquid in which the crystal grew. Original pressure
> was somehow derived from other factors. I forgot. [/Aside]

Crazy! I haven't a clue how those environmental factors could possibly be sussed
out. That's hacking, as far as I'm concerned... Physical hacking, not digital,
which is even cooler. She sounds like an awesome woman :)

> But, those fluid inclusions are difficult to model. I was thinking about
> clouds of bubbles in liquid (there are a couple of scene files drifting
> around in the pov world; I think I have a couple of those somewhere)
> using a gaussian distribution scheme...

Inclusions are pretty much the main impediment to making better mineral renders.

And inclusions take on many forms. Not all exhibit crystalline features when
viewed with the naked eye (e.g. light reflecting at certain angles only). Some
do, though. I had (or still have) a Herkimer 'diamond' that apparently has an
inclusion in the shape if a tiny quartz crystal. The bubble really looks like a
tiny, doubly-terminated quartz crystal. I'll have to take a photo of that.

> > Besides the symmetry, another thing I noticed about the crystal libraries in KS
> > is that the secondary and tertiary faces (modifications) tend to be somewhat
> > exaggerated. (...)
> >
> Yes, I have been wondering about that. Not being an expert, I have been
> hesitating between the different models proposed.

Eh, nothing is written in stone. (Haha, except stones.) But there are always
outliers to these things. Depending on the conditions in which a chemical is
grown, modifications may become more or less prominent. You never know.

Sam

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"Samuel B." <stb### [at] hotmailcom> wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:

> > [Aside] in a very distant past, my wife did a study on fluid inclusions
> > in quartz crystals from Greece. She could, by cooling the crystals in
> > liquid nitrogen and then slow heating, determine the original
> > temperature of the liquid in which the crystal grew. Original pressure
> > was somehow derived from other factors. I forgot. [/Aside]
>
> Crazy! I haven't a clue how those environmental factors could possibly be sussed
> out.

I would imagine that it might have something to do with the phase diagram of the
material.  Freeze the material so that it's solid, and then do a melting-point
test by the usual slow heating.  Maybe there's some specialized
pressure-temperature nomograph that's been developed for this type of thing...

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Op 29-10-2021 om 12:49 schreef Bald Eagle:
> "Samuel B." <stb### [at] hotmailcom> wrote:
>> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>>> [Aside] in a very distant past, my wife did a study on fluid inclusions
>>> in quartz crystals from Greece. She could, by cooling the crystals in
>>> liquid nitrogen and then slow heating, determine the original
>>> temperature of the liquid in which the crystal grew. Original pressure
>>> was somehow derived from other factors. I forgot. [/Aside]
>>
>> Crazy! I haven't a clue how those environmental factors could possibly be sussed
>> out.
> 
> I would imagine that it might have something to do with the phase diagram of the
> material.  Freeze the material so that it's solid, and then do a melting-point
> test by the usual slow heating.  Maybe there's some specialized
> pressure-temperature nomograph that's been developed for this type of thing...
> 
Yes, I think it was phase changes indeed. All that happened 45 years ago...

-- 
Thomas

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this is a randomised version of the apophyllite crystal. I also changed 
the light probe and tweaked the scattering media (which still remains a 
second choice), and brought the photon spacing to more natural levels 
(0.01).

-- 
Thomas

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