Hi(gh)!

Following a thread on Jupiter images on p.o-t, I started to model some 
basic gas giant textures based on this (non-POV-Ray) tutorial:
https://www.seedofandromeda.com/blogs/49-procedural-gas-giant-rendering-with-gpu-noise
with color suggestions gleaned from here: 
http://visions2200.com/Articles/ExtrasolarSpeculations.html (the chapter 
"Color, Albedo and Temperature), I made a "cold Jovian" gas giant as 
attached below...

...but how do I get realistic storm systems? The ones at "Seed of 
Andromeda" do not look very convincing, they would have to drag in 
clouds in a spiralling rather than a straight way (like with the 
black_hole warp of POV-Ray). Is there some trick to achieve a "spiral warp"?

See you in Khyberspace!

Yadgar

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Attachments:
Download 'cold_jovian_gas_giant.png' (534 KB)

Preview of image 'cold_jovian_gas_giant.png'

On 14-7-2018 0:35, Jörg "Yadgar" Bleimann wrote:
> ...but how do I get realistic storm systems? The ones at "Seed of 
> Andromeda" do not look very convincing, they would have to drag in 
> clouds in a spiralling rather than a straight way (like with the 
> black_hole warp of POV-Ray). Is there some trick to achieve a "spiral 
> warp"?
> 

Just thinking aloud, not verified (yet) is it possible to add 'rotate 
<....>' to a black hole warp within the warp block?

-- 
Thomas

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Hi(gh)!

On 14.07.2018 08:46, Thomas de Groot wrote:

> Just thinking aloud, not verified (yet) is it possible to add 'rotate 
> <....>' to a black hole warp within the warp block?

Probably not, I tried scaling (to get more elongated warps), but got an 
error message! And, rotating would change only the orientation of the 
warp, not its internal structure...

See you in Khyberspace!

Yadgar

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On 14-7-2018 11:34, Jörg "Yadgar" Bleimann wrote:
> Hi(gh)!
> 
> On 14.07.2018 08:46, Thomas de Groot wrote:
> 
>> Just thinking aloud, not verified (yet) is it possible to add 'rotate 
>> <....>' to a black hole warp within the warp block?
> 
> Probably not, I tried scaling (to get more elongated warps), but got an 
> error message! And, rotating would change only the orientation of the 
> warp, not its internal structure...
> 

yes... You are right; I was thinking along another line though which 
involved an imaginary rotation/deformation of the pattern. No there of 
course.

This is a problem. One would need something like the cylindrical warp 
applied to the individual black holes... oh hell! I don't know how to 
solve this... :-(

-- 
Thomas

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I don't have anything to suggest in terms of adapting or implementing this, but
I was just looking around and found this.

http://news.povray.org/povray.binaries.images/message/%3C4cd5e4f2%40news.povray.org%3E/#%3C4cd5e4f2%40news.povray.org%3
E

Not sure if that's of any use at all....

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On 14-7-2018 21:10, Bald Eagle wrote:
> I don't have anything to suggest in terms of adapting or implementing this, but
> I was just looking around and found this.
> 
>
http://news.povray.org/povray.binaries.images/message/%3C4cd5e4f2%40news.povray.org%3E/#%3C4cd5e4f2%40news.povray.org%3
> E
> 
> Not sure if that's of any use at all....
> 
> 
> 

The problem is: how would you apply this to a black hole warp? I 
mentioned the cylindrical warp, but with spiral1 or spiral2 the problem 
would be the same. I have no idea at the moment.

-- 
Thomas

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

> The problem is: how would you apply this to a black hole warp? I
> mentioned the cylindrical warp, but with spiral1 or spiral2 the problem
> would be the same. I have no idea at the moment.

Right.   Just throwing ideas out to spark some brainstorming.
I'm assuming that at some point, someone will go "AHA!"

See "Black Hole" and "Tornado"
http://www.bugman123.com/Renderings/index.html

and let us not forget:
http://www.f-lohmueller.de/pov_tut/backgrnd/p_wat4.htm

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On 15-7-2018 23:45, Bald Eagle wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>> The problem is: how would you apply this to a black hole warp? I
>> mentioned the cylindrical warp, but with spiral1 or spiral2 the problem
>> would be the same. I have no idea at the moment.
> 
> Right.   Just throwing ideas out to spark some brainstorming.
> I'm assuming that at some point, someone will go "AHA!"
> 
> See "Black Hole" and "Tornado"
> http://www.bugman123.com/Renderings/index.html
> 
> and let us not forget:
> http://www.f-lohmueller.de/pov_tut/backgrnd/p_wat4.htm
> 

Yes, there are some pretty good whirlpool examples around in POV 
space... :-)

It is always what there is not that we want most urgently! ;-)

-- 
Thomas

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Hi(gh)!

On 15.07.2018 23:45, Bald Eagle wrote:

> Right.   Just throwing ideas out to spark some brainstorming.
> I'm assuming that at some point, someone will go "AHA!"
> 
> See "Black Hole" and "Tornado"
> http://www.bugman123.com/Renderings/index.html
> 
> and let us not forget:
> http://www.f-lohmueller.de/pov_tut/backgrnd/p_wat4.htm
> 
...but I need (for the time being - later on I would model real cloud 
layers with media) a kind of pattern modifier, not a 3D object!

See you in Khyberspace!

Yadgar

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One idea would be to use POV-Ray's BOXED pattern-- with a pigment_map composed
of *multiple* (averaged?) SPIRAL patterns inside it, each with some appropriate
colors and warp{turbulence...}-- as a way to apply separate 'decals' to various
places on the already-textured planet surface. (The 'outside' of the BOXED
pattern(s) could fade to transparency, so as not to look like the storms are
simply stuck on.) The idea is certainly not as 'realistic' as true fluid
dynamics, but it might work.

Post a reply to this message

Not followed this through, but I begin to think that a solution might be 
found in the use of fractal patterns 
http://wiki.povray.org/content/Reference:Fractal_Pattern. Exponent 2 of 
the Julia set looks suspiciously like what you are looking for. No idea 
(yet) how to implement this however....

-- 
Thomas

Post a reply to this message

Le 18-07-17 à 06:54, Kenneth a écrit :
> One idea would be to use POV-Ray's BOXED pattern-- with a pigment_map composed
> of *multiple* (averaged?) SPIRAL patterns inside it, each with some appropriate
> colors and warp{turbulence...}-- as a way to apply separate 'decals' to various
> places on the already-textured planet surface. (The 'outside' of the BOXED
> pattern(s) could fade to transparency, so as not to look like the storms are
> simply stuck on.) The idea is certainly not as 'realistic' as true fluid
> dynamics, but it might work.
> 

Instead of the boxed pattern, I'd use the shperical one. The, yes, use a 
spiral pattern, or a few averaged ones.
spiral 25 scale Something rotate Rotation


Alain

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Alain <kua### [at] videotronca> wrote:

> >
>
> Instead of the boxed pattern, I'd use the shperical one....

Yes, that sounds better than a 'square' BOXED pattern.

Post a reply to this message

> ...but how do I get realistic storm systems? The ones at "Seed of
> Andromeda" do not look very convincing, they would have to drag in
> clouds in a spiralling rather than a straight way (like with the
> black_hole warp of POV-Ray). Is there some trick to achieve a "spiral warp"?

So, I was clicking around on my new, minty-fresh Linux Mint install, and came
across the screen savers.  Most were written by Jamie Zawinski / jwz and the
source code for most or all of them are at:

https://www.jwz.org/xscreensaver/download.html

There are some very interesting ideas, implementations, and effects, and
"Distort" seemed to have a spiral effect.
The screen saver menu is a rich source of information, as each choice has a
description and URLs of articles on the web about the underlying system.

The specific URLs for the Distort screensaver were
https://en.wikipedia.org/wiki/Euler_equations_(fluid_dynamics)
and
https://en.wikipedia.org/wiki/Inviscid_flow

There are LOTS of very nice algorithms illustrated that have been talked abut
here in the forum, and might be likely to spark new interest in old topics.

Post a reply to this message

This is just here for related brain and eye candy.
I was impressed by some of the tools that Mathematica has to process data, and
the manner in which the author sidesteps a roadblock or two with very practical
workarounds.

Enjoy  :)

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I have made some space and planetary scenes. A spiral warp would be nice 
for galaxies and hurricanes.


Mike


On 7/13/2018 6:35 PM, Jörg "Yadgar" Bleimann wrote:
> Hi(gh)!
> 
> Following a thread on Jupiter images on p.o-t, I started to model some 
> basic gas giant textures based on this (non-POV-Ray) tutorial:
>
https://www.seedofandromeda.com/blogs/49-procedural-gas-giant-rendering-with-gpu-noise

> 
> with color suggestions gleaned from here: 
> http://visions2200.com/Articles/ExtrasolarSpeculations.html (the chapter 
> "Color, Albedo and Temperature), I made a "cold Jovian" gas giant as 
> attached below...
> 
> ...but how do I get realistic storm systems? The ones at "Seed of 
> Andromeda" do not look very convincing, they would have to drag in 
> clouds in a spiralling rather than a straight way (like with the 
> black_hole warp of POV-Ray). Is there some trick to achieve a "spiral 
> warp"?
> 
> See you in Khyberspace!
> 
> Yadgar

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I think I found what looks to be some workable equations at:

https://people.sc.fsu.edu/~jburkardt/cpp_src/navier_stokes_2d_exact/navier_stokes_2d_exact.html


If you look at the png image, and then the source code for the vortex solution,
you'll notice that the code simply runs through an loop to evaluate the formula
over the <x, y> values of a unit square grid.
So, since POV-Ray "does the looping" when applying a pattern, that part of the
code is redundant, which just leave us with 3 equations.

The mental block is afflicting me with how to apply this, and how a warp is
different than a pattern.

(not having ever used gnuplot is a small problem as well)

Cue someone stepping in with the crayons and sock puppets to explain how I'd
make a spiral warp using functions, and how I'd visualize this.

Currently, my understanding is that a warp is akin to a translation or
phase-shift, where what's going on at the current point <x,y,z> is redefined as
what's going on at some other point, as defined by the code/function of the
warp.

I don't FULLY grasp the whole thing, so I'll try to describe it, and maybe
someone who sees the whole picture can correct me where I'm wrong.

I'll try to describe what I think happens in the following black hole warp code.
There's a "block" thing going on which I can only assume is for octants or
figuring out where in a repeat warp the black hole is being used.

Then in the actual application, you have a radius and a strength that are
specified.  So first, the distance of <x, y, z> from the center of the black
hole is determined.  Then that gets what I call "flipped" - if the distance is
1, it's now zero, and if it's 0, it's now 1.
That gets done in my illustrative function
#declare Limit = function {(Radius-Dist(x,y,z))...
and then it gets expressed as a proportion of the radius of the effect:
".../Radius}"
The result being that the black hole effect is strongest at the center, and
dropping off to zero near the radius.


#declare Radius = 0.2;
#declare Dist = function {sqrt(pow(x,2)+pow(y,2)+pow(z,2))}
#declare Limit = function {(Radius-Dist(x,y,z))/Radius}
#declare Warp = function {select( Limit(x,y,z), 0, 0, 1)}

that gets altered exponentially ...

.... and then the resulting scalar value gets used as a modifier of the <x, y,
z>, in Vector.h.

if we were physically moving points, this would be:

#declare Vector = <x, y, z>;
#declare NewVector = <x, y, z> + scalar * <a, b, c>;

Not really sure how vector <a, b, c> is defined, but let's keep that in the
black box for now.

But this is all mathematical, and the coordinates always stay the same, don't
they?  So what's really happening is that we're modifying the input of a pattern
or brightness or normal function so that it's behaving as if it were being
evaluated at another, point.  The FUNCTION is shifted by the warp.

If you look through Mike Williams' isosurface tutorial
http://www.econym.demon.co.uk/isotut/

the way to do this with a function is to "do the opposite"
to translate the effect in the +x direction, we subtract the translation from
the x term so that we are evaluating the function at (x-c).
Picture pulling a parabola, y=pow(x,2) to the right.
We grab the y value at (x-c) and pull it over to x, thus shifting it in the +x
direction.



I can only assume that if I want to model a warp, let's say as a density
function in a media (since that's been successful so far)
then I would use the warp to modify the effect of a pattern function.




The following is for a Black Hole Warp from warps.cpp:

case BLACK_HOLE_WARP:
Black_Hole = reinterpret_cast<BLACK_HOLE *>(Warp) ;
Assign_Vector (Center, Black_Hole->Center) ;

if (Black_Hole->Repeat)
{
/* first, get the block number we're in for each dimension  */
/* block numbers are (currently) calculated relative to 0   */
/* we use floor () since it correctly returns -1 for the
first block below 0 in each axis                         */
/* one final point - we could run into overflow problems if
the repeat vector was small and the scene very large.    */
if (Black_Hole->Repeat_Vector [X] >= EPSILON)
blockX = (int) floor (TPoint [X] / Black_Hole->Repeat_Vector [X]) ;

if (Black_Hole->Repeat_Vector [Y] >= EPSILON)
blockY = (int) floor (TPoint [Y] / Black_Hole->Repeat_Vector [Y]) ;

if (Black_Hole->Repeat_Vector [Z] >= EPSILON)
blockZ = (int) floor (TPoint [Z] / Black_Hole->Repeat_Vector [Z]) ;

if (Black_Hole->Uncertain)
{
/* if the position is uncertain calculate the new one first */
/* this will allow the same numbers to be returned by frand */

int seed = Hash3d (blockX, blockY, blockZ);
Center [X] += WarpRands(seed) * Black_Hole->Uncertainty_Vector [X] ;
Center [Y] += WarpRands(seed + 1) * Black_Hole->Uncertainty_Vector [Y] ;
Center [Z] += WarpRands(seed + 2) * Black_Hole->Uncertainty_Vector [Z] ;
}

Center [X] += Black_Hole->Repeat_Vector [X] * blockX ;
Center [Y] += Black_Hole->Repeat_Vector [Y] * blockY ;
Center [Z] += Black_Hole->Repeat_Vector [Z] * blockZ ;
}

VSub (Delta, TPoint, Center) ;
VLength (Length, Delta) ;

/* Length is the distance from the centre of the black hole */
if (Length >= Black_Hole->Radius) break ;

if (Black_Hole->Type == 0)
{
/* now convert the length to a proportion (0 to 1) that the point
is from the edge of the black hole. a point on the perimeter
of the black hole will be 0.0 ; a point at the centre will be
1.0 ; a point exactly halfway will be 0.5, and so forth. */
Length = (Black_Hole->Radius - Length) / Black_Hole->Radius ;

/* Strength is the magnitude of the transformation effect. firstly,
apply the Power variable to Length. this is meant to provide a
means of controlling how fast the power of the Black Hole falls
off from its centre. if Power is 2.0, then the effect is inverse
square. increasing power will cause the Black Hole to be a lot
weaker in its effect towards its perimeter.

finally we multiply Strength with the Black Hole's Strength
variable. if the resultant value exceeds 1.0 we clip it to 1.0.
this means a point will never be transformed by more than its
original distance from the centre. the result of this clipping
is that you will have an 'exclusion' area near the centre of
the black hole where all points whose final value exceeded or
equalled 1.0 were moved by a fixed amount. this only happens
if the Strength value of the Black Hole was greater than one. */

Strength = pow (Length, Black_Hole->Power) * Black_Hole->Strength ;
if (Strength > 1.0) Strength = 1.0 ;

/* if the Black Hole is inverted, it gives the impression of 'push-
ing' the pattern away from its centre. otherwise it sucks. */
VScaleEq (Delta, Black_Hole->Inverted ? -Strength : Strength) ;

/* add the scaled Delta to the input point to end up with TPoint. */
VAddEq (TPoint, Delta) ;
}
break;

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Here's a real first stab at doing the right thing:

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Attachments:
Download 'spiralwarp.png' (263 KB)

Preview of image 'spiralwarp.png'

And I think this captures the essence of it.

Whee!

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Attachments:
Download 'spiralwarp.png' (62 KB)

Preview of image 'spiralwarp.png'

On 23-7-2018 0:45, Bald Eagle wrote:
> And I think this captures the essence of it.
> 
> Whee!
> 

But.... concentric shells... those are /not/ storm patterns, are they? :-/

-- 
Thomas

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

> But.... concentric shells... those are /not/ storm patterns, are they? :-/

Not exactly - but they are a type of vortex that's generated from fluid dynamics
equations ... so I would imagine they appear somewhere.

Still working on getting an actual bona-fide spiral shape, but I was happy that
with the weekend rapidly slipping away, I was able to get most of the key pieces
to the method strung together.

Never ever ever ever ever ever ever ever give up.

Hopefully I'll get the code cleaned up and I'll discover some good (x,y)
equations to do exactly what I want - both with control of the internal shape of
the warp, as well as the smooth blending of the edges of the perturbation with
the rest of the scene.

Post a reply to this message

On 23-7-2018 12:33, Bald Eagle wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>> But.... concentric shells... those are /not/ storm patterns, are they? :-/
> 
> Not exactly - but they are a type of vortex that's generated from fluid dynamics
> equations ... so I would imagine they appear somewhere.
> 
> Still working on getting an actual bona-fide spiral shape, but I was happy that
> with the weekend rapidly slipping away, I was able to get most of the key pieces
> to the method strung together.
> 
> Never ever ever ever ever ever ever ever give up.
> 
> Hopefully I'll get the code cleaned up and I'll discover some good (x,y)
> equations to do exactly what I want - both with control of the internal shape of
> the warp, as well as the smooth blending of the edges of the perturbation with
> the rest of the scene.
> 

I am watching with interest.

-- 
Thomas

Post a reply to this message

On 23/07/2018 11:44, Thomas de Groot wrote:
> On 23-7-2018 12:33, Bald Eagle wrote:
>> Thomas de Groot <tho### [at] degrootorg> wrote:
>>
>>> But.... concentric shells... those are /not/ storm patterns, are 
>>> they? :-/
>>
>> Not exactly - but they are a type of vortex that's generated from 
>> fluid dynamics
>> equations ... so I would imagine they appear somewhere.
>>
>> Still working on getting an actual bona-fide spiral shape, but I was 
>> happy that
>> with the weekend rapidly slipping away, I was able to get most of the 
>> key pieces
>> to the method strung together.
>>
>> Never ever ever ever ever ever ever ever give up.
>>
>> Hopefully I'll get the code cleaned up and I'll discover some good (x,y)
>> equations to do exactly what I want - both with control of the 
>> internal shape of
>> the warp, as well as the smooth blending of the edges of the 
>> perturbation with
>> the rest of the scene.
>>
> 
> I am watching with interest.
> 

So am I.

-- 

Regards
     Stephen

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In this next philosophical installment, I will address an aspect of this which I
had suspected, and speculate on the manner of successfully implementing a
desired pattern.

An equation may be expressed or visualized as a point, line, curve, or surface -
but a warp in the shape of that equation - I do not believe - can be obtained by
perturbing a pattern by that equation.

Instead, the pattern needs to be perturbed by the equation in reverse.  Or as
Mike Williams and POV-Ray, and Matrix Algebra would put it - as the inverse.

http://www.econym.demon.co.uk/isotut/substitute.htm

Shear
It's a bit more dificult to produce a particular shear transformation, because
the values that we need to use in the variable substitution need to be the
inverse of those normally used to generate the shear. We could calculate the
inverse of the transformation matrix by hand, but it is possible to get POV-Ray
to do it for us.

We first create a shear transformation, then declare a transformation function
using its inverse.

#include "transforms.inc"
#declare TR=Shear_Trans(<-0.5,0.5,0.5>,<1.1,0,-0.3>,<-0.3,0.5,0>)
#declare TRFI = function {transform {TR inverse}}

Now we can apply that transformation function to the unit vectors which gives us
the values we need for the substitution. However, we can't use vectors from
inside an isosurface function, so we have to extract the x, y and z values of
each of those vectors outside the isosurface.

#declare A=TRFI(1,0,0);
#declare B=TRFI(0,1,0);
#declare C=TRFI(0,0,1);

#declare Ax=A.x;#declare Bx=B.x;#declare Cx=C.x;
#declare Ay=A.y;#declare By=B.y;#declare Cy=C.y;
#declare Az=A.z;#declare Bz=B.z;#declare Cz=C.z;

We can now use these scalar values in the variable substitution.

function { F(Ax*x+Bx*y+Cx*z, Ay*x+By*y+Cy*z, Az*x+Bz*y+Cz*z) }

The image on the left shows two boxes. One of them is sheared by variable
substitution and the other is sheared with the equivalent conventional shear
transform.

The same method can be used for combinations of shear, rotation and scale
operations. It doesn't seem to work for transformations that involve
translation, but we already know how to do that.


https://www.mathsisfun.com/algebra/matrix-inverse.html

So, I have a few ideas as to the type of spiral / vortex that might be
interesting, however the specific type that I think might be currently sought
after is based on the Kelvin-Helmholtz instability.


https://nylander.wordpress.com/category/physics/fluids/
http://bugman123.com/FluidMotion/KelvinHelmholtz1.m1v
https://en.wikipedia.org/wiki/Kelvin%E2%80%93Helmholtz_instability

Understanding the concepts behind visualizing a vector field I think is
important here, as is bridging the gaps and filling in the missing steps of math
texts that leave you hanging.


Let's say we're talking about some time-dependent fluid dynamics equations that
describe the genesis of a cyclone.  Well, thinking about how that would _look_,
the points - the colors and textures and brightnesses of the pixels would move
along as the clock of the animation incremented.
I think the key to implementing a warp is doing exactly the opposite. The point
at time (t) needs to "inherit" the characteristics of the point in the equation
at t=0.

So, for the time being, I'll probably be (slowly) coding up inverse transforms,
trying out various spiral equations (entries welcome) and seeing if I can come
up with some sort of fairly functional Warp Lab / Playground.

If anyone has any experience in using Mathematica or Matlab, converting some of
the code on Nylander's page would be a nice boost forward.

If there are any computer graphics texts or sites explaining how to construct a
WARP in a texture - that would be some good reading as well.

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On 23-7-2018 0:45, Bald Eagle wrote:
> And I think this captures the essence of it.
> 
> Whee!
> 

Have you looked at this page?
http://bugman123.com/FluidMotion/index.html
That seems to be what is needed...

-- 
Thomas

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http://thevirtualheart.org/GPU/2dkmodelF.html

view-source:http://thevirtualheart.org/GPU/2dkmodelF.html

http://thevirtualheart.org/GPU/WebGL_GPU_spiral_waves_heart.html

Post a reply to this message

On 1-8-2018 18:32, Bald Eagle wrote:
> http://thevirtualheart.org/GPU/2dkmodelF.html
> 
> view-source:http://thevirtualheart.org/GPU/2dkmodelF.html
> 
> http://thevirtualheart.org/GPU/WebGL_GPU_spiral_waves_heart.html
> 

Hmmm yes. Getting closer although I still miss a genuine coriolis effect.

-- 
Thomas

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