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Alain Martel <kua### [at] videotron ca> wrote:
> Tried projected_through with a filtering pattern creating a gradient. It
> don't work. You get a warning about projected_through requiring a
> texture-less object, and the pigment or pattern is ignored.
Yeah - RTFM shows that it doesn't do what I had thought it did.
https://wiki.povray.org/content/Reference:Light_Source#Projected_Through
Projected Through
You can use projected_through with any type of light source. Any object can be
used, provided it has been declared beforehand. Projecting a light through an
object can be thought of as the opposite of shadowing, in that only the light
rays that hit the projected through object will contribute to the scene. This
also works with area lights producing spots of light with soft edges. Any
objects between the light and the projected through object will not cast
shadows, additionally any surface within the projected through object will not
cast shadows. Any textures or interiors on the object will be stripped and the
object will not show up in the scene.
The syntax is as follows:
light_source {
LOCATION_VECTOR, COLOR
[LIGHT_SOURCE_ITEMS...]
projected_through { OBJECT }
}
Maybe use a disk with a cylindrical pattern and a gradient, or a sphere with an
onion and a gradient.
We don't actually have any inbuilt pattern that would give a conical gradient,
do we?
Maybe use a cylindrical gradient with a spherical warp.
Put the camera in the center of it.
Then just write a function that limits the locus of the gradient and gives the
right color-mapping for the glory effect.
Post a reply to this message
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And here you go:
http://www.philiplaven.com/Publications/AO-42-03-p436.pdf
http://www.philiplaven.com/mieplot.htm
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"Bald Eagle" <cre### [at] netscapenet> wrote:
> And here you go:
>
> http://www.philiplaven.com/Publications/AO-42-03-p436.pdf
>
> http://www.philiplaven.com/mieplot.htm
http://www.philiplaven.com/p4.html
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"Bald Eagle" <cre### [at] netscapenet> wrote:
> Alain Martel <kua### [at] videotronca> wrote:
>
> > Tried projected_through with a filtering pattern creating a gradient. It
> > don't work. You get a warning about projected_through requiring a
> > texture-less object, and the pigment or pattern is ignored.
>
> Yeah - RTFM shows that it doesn't do what I had thought it did.
>
> https://wiki.povray.org/content/Reference:Light_Source#Projected_Through
>
> Projected Through
> You can use projected_through with any type of light source. Any object can be
> used, provided it has been declared beforehand. Projecting a light through an
> object can be thought of as the opposite of shadowing, in that only the light
> rays that hit the projected through object will contribute to the scene. This
> also works with area lights producing spots of light with soft edges. Any
> objects between the light and the projected through object will not cast
> shadows, additionally any surface within the projected through object will not
> cast shadows. Any textures or interiors on the object will be stripped and the
> object will not show up in the scene.
>
> The syntax is as follows:
>
> light_source {
> LOCATION_VECTOR, COLOR
> [LIGHT_SOURCE_ITEMS...]
> projected_through { OBJECT }
> }
>
>
> Maybe use a disk with a cylindrical pattern and a gradient, or a sphere with an
> onion and a gradient.
>
Here's something I tried.
Post a reply to this message
Attachments:
Download 'lightplay.jpg' (19 KB)
Preview of image 'lightplay.jpg'
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I haven't done any more work on the diffraction stuff, but I did happen across
an interesting parametric equation describing the real shape of a falling
raindrop.
r = Sigma [A * ( 1 + Cn * cos(Cn * Theta)]
with a table of 8 C values for droplet radii ranging from 0 to 3mm
Had a devil of a time working that all out so that the values get linearly
interpolated for any given raindrop size.
Then I:
plotted it out with spheres,
messed up the parametric {},
tried to convert the parametric into an isosurface,
tried to render a sor {};
fixed my parametric {},
finally used a lathe {}, and added an ior of 1.33
I generated 100 raindrops of each size and randomly translated them.
- BW
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Attachments:
Download 'raindrop.png' (931 KB)
Preview of image 'raindrop.png'
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Cousin Ricky <ric### [at] yahoocom> wrote:
> Many years ago, alphaQuad aka Melody issued a glory ping pong challenge,
> but was quite unsuccessful.
I had some very nice exchanges with the friendly Philip Laven, and we talked
about how simulating the optics was "fiendishly complicated", and how here on
the forum we'd like to merely simulate the effect as best we could without
approximating the underlying plane wave interference.
So, for the moment, I noticed that POV-Ray has an inbuilt rainbow atmospheric
effect.
https://wiki.povray.org/content/Reference:Rainbow
So I took the image from
http://www.philiplaven.com/Mie-r10-175-180-0p01-300col.jpg
(at http://www.philiplaven.com/p2c1.html)
Which already has the rgb values for the glory laid out in a linear form, and
plugged that (as a cropped version) as an image_map into a pigment and then into
a function, and used a loop to define my color map entries using the 0-1 index
as an argument to the function.
Then I used that color_map for the rainbow, tweaked some parameters, stuck a
plane with a cloud pigment behind it, and there we go.
Important note: the rainbow must make use of a mechanism very much like media,
since the plane needed to be hollow to see the rainbow. (One can also just flip
the plane normal using the inverse keyword)
I'm trying to figure out how to cast a shadow _through_ scattering media to
simulate the Brocken Spectre, but haven't figured that part out yet.
I might need to alter the color_map function to change the fading effect, but it
looks passable for now.
- BW
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Attachments:
Download 'glory2.png' (219 KB)
Preview of image 'glory2.png'
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OK, I got the shadow, I just need to figure out how to get that LONG shadow that
goes all the way from the camera and out to the "orthographic shadow".
- BW
Post a reply to this message
Attachments:
Download 'glory2.png' (266 KB)
Preview of image 'glory2.png'
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From: William F Pokorny
Subject: Re: Glories, POV-Ray, and diffraction
Date: 26 Feb 2025 13:08:23
Message: <67bf5897@news.povray.org>
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On 2/20/25 19:07, Bald Eagle wrote:
> I'm trying to figure out how to cast a shadow_through_ scattering media to
> simulate the Brocken Spectre, but haven't figured that part out yet.
Playing with an idea.
The attached image uses multiple isosurfaces as colored dust. I used
yuqk's new f_popnrm_rnoise() to break shapes up rather than my usual
method with extreme turbulence blowing isosurfaces apart.
It kinda of works as far as I've gotten...
The thought - still untested - is given these particles exist, it should
be I can project light from the backside 'through' them and into
scattering media between the camera and the particles.
The effect counts on fairly heavy AA (it's effectively part of the
sampling / color-blending). With media too - this method might get
really slow, but we'll see.
Off to do some RL stuff, but I'll try and get back and try the projected
light / media part of it soon.
Bill P.
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Attachments:
Download 'try00.jpg' (66 KB)
Preview of image 'try00.jpg'
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William F Pokorny <ano### [at] anonymousorg> wrote:
> On 2/20/25 19:07, Bald Eagle wrote:
> > I'm trying to figure out how to cast a shadow_through_ scattering media to
> > simulate the Brocken Spectre, but haven't figured that part out yet.
>
> Playing with an idea.
Nice.
However for the glory, Philip will be quite cross is you treat it like a
diffraction effect.
It's not - it's a plane wave interference effect.
The colors that you get are therefore sort of reversed from a regular rainbow.
Image_map attached.
- BW
Post a reply to this message
Attachments:
Download 'mie-r10-175-180-0p01-300col.jpg' (7 KB)
Preview of image 'mie-r10-175-180-0p01-300col.jpg'
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On 2/26/25 18:08, Bald Eagle wrote:
> The colors that you get are therefore sort of reversed from a regular rainbow.
>
> Image_map attached.
Thanks, Bill, for posting the image_map image with the colors.
Attached is an image where the light source was moved behind the plane
with the wrinkles pattern clouds. I used the outer most of the six,
color, isosurface dust, rings as the projected through shape. The light
rays magically pop through the blocking plane and shoot out of a
gazillion dust particles on the other side!
It is slow. Right at two hours on my old Intel i3 CPU. It's not all due
scattering media; My leaving the plane's pigment as a wrinkles pattern
was costly. A stored image mapped to the plane would be faster.
More work would be needed to make it look somewhat realistic to any
given real world phenomenon. The image is generated 'looking the wrong
way', for example, but the method has potential for faking effects like
Glories I think.
Bill P.
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Attachments:
Download 'try01.jpg' (54 KB)
Preview of image 'try01.jpg'
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