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Hi Tracers!
I'm back with a revisited version of my orbital Earth picture... now the
atmosphere fringe (at least to me) looks perfect, and I started with the
next step, i. e. adding a cloud layer around Earth.
Preliminarily, I did that with a simple sphere about 0.005 units (5 kms
in my chosen scale) larger that Earth itself, I hope that later on, I
might be able to use a CSG difference object filled with media.
But even with this simpler version, a new problem arises: which
pattern/noise modification to choose to get halfway realistic cloud
coverage, i. e. cyclonic/anticyclonic whirls? I tried a whole range of
patterns, from agate to spiral1, usually frequency 1, with more or less
turbulence, scaled between 0.1 and 1 and with different scopes within
the color map for non-transparent white.
Also, I thought about some relief for my clouds to emulate cumuli
structures... up to now, I've tried bumps and dents, but none of them
yielded satisfying results.
The texture code for the image attached here:
#declare Earth_Clouds =
material // Earth Clouds, Medium Coverage
{
texture
{
pigment
{
spiral1 10
color_map
{
[ 0.0 rgbft <0.0, 0.0, 0.0, 1.0, 1> ]
[ 0.35 rgbft <0, 0, 0, 1, 1>]
[ 0.42 rgbft <1,1,1,0,0>]
[ 0.63 rgbft <1,1,1,0,0>]
[ 0.70 rgbft <0, 0, 0, 1, 1>]
[ 1.0 rgbft <0.0, 0.0, 0.0, 1.0, 1> ]
}
turbulence 2
frequency 1
octaves 6
ramp_wave
scale 1
}
normal
{
dents
scale 0.003
}
}
}
See you in Khyberspace!
Yadgar
Post a reply to this message
Attachments:
Download 'siberian summer.jpg' (195 KB)
Preview of image 'siberian summer.jpg'
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Hello Yadgar,
you could simply use a separate real cloud map. I've got one on my harddisk.
But that's probably not in the *spirit* of the game?
Claudius
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Yadgar wrote:
>
[...]
>
> But even with this simpler version, a new problem arises: which
> pattern/noise modification to choose to get halfway realistic cloud
> coverage, i. e. cyclonic/anticyclonic whirls? I tried a whole range of
> patterns, from agate to spiral1, usually frequency 1, with more or less
> turbulence, scaled between 0.1 and 1 and with different scopes within
> the color map for non-transparent white.
>
Realistic clouds from above are a difficult thing, you should try using warps
for local changes of the pattern. A turbulent bozo pattern is often a good
start for cloud structures, but you could also try something else.
> Also, I thought about some relief for my clouds to emulate cumuli
> structures... up to now, I've tried bumps and dents, but none of them
> yielded satisfying results.
>
You have to remember, that normal statements only change the normal vectors but
not the geometry of the clouds. For volume either use media of several cloud
layers.
Concerning the ground image map, i wonder whether the white parts are already
clouds. Furthermore i would suggest interpolation for getting rid of the grid
structures and maybe you should consider real mountains with an isosurface. (it
looks somewhat flat right now)
The atmosphere looks good, but i wonder about the height ratio: if the clouds
are 5 km high, the atmosphere seems to be visible up to more than 100 km which
is too high IMO.
Christoph
--
Christoph Hormann <chr### [at] gmx de>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/
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From: Yadgar
Subject: Re: Siberian Summer (195K) - realistic cloud swirls?
Date: 1 Oct 2000 17:21:26
Message: <39D78150.4D8CB00C@ndh.net>
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Hi Christoph and all others!
Christoph Hormann schrieb:
> Realistic clouds from above are a difficult thing, you should try using warps
> for local changes of the pattern. A turbulent bozo pattern is often a good
> start for cloud structures, but you could also try something else.
>
Warps? Never heard of them... how are they implemented?
<half an hour later...>
Ah, I found it in my PoV manual... from browsing through the "Warps" section, it
looks like the black_hole warp would meet my needs best... but how is the position
of each warp calculated respective to the actual texture on the object (which might
be scaled, rotated and translated afterwards)?
Do I have to scale etc. also the warp?
> Concerning the ground image map, i wonder whether the white parts are already
> clouds. Furthermore i would suggest interpolation for getting rid of the grid
> structures and maybe you should consider real mountains with an isosurface. (it
> looks somewhat flat right now)
Yes, I tried interpolate 2... looks much better! The white parts are not clouds, but
mountains covered with perennial snow (it's Eastern Siberia!)
Real mountains with an isosurface... you think of wrapping a heightfield around the
Earth sphere? I'm familiar with tools like DMesh or John Beale's ORB... they work
pretty well with asteroids, but with a real planet, I'm skeptical... I in fact have
an 8-bit greyscale heightfield of Earth's land surface on my harddisk, but as its
scale is still comparatively small (4320 by 2160 pixels) and the mountain ranges
visible here are in reality hardly higher than 3.000 meters (except for some single
volcanoes on Kamchatka, on the right limb), I would have to exaggerate the
heightfield's altitude dimension considerably to see any structures at all!
And as my machine is "only" an AMD K6-II-400 (currently slowed down to 300) with 64
MB RAM, I would not be able to make any use of much larger heightfields...
> The atmosphere looks good, but i wonder about the height ratio: if the clouds
> are 5 km high, the atmosphere seems to be visible up to more than 100 km which
> is too high IMO.
>
My atmosphere sphere (filled with blue media) in fact reaches 200 km high... but
when I compare my image to real orbital views, it looks correct to me!
See you in Khyberspace!
Yadgar
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From: Anton Sherwood
Subject: Re: Siberian Summer (195K) - realistic cloud swirls?
Date: 1 Oct 2000 23:16:41
Message: <39D7FFB6.76B31B6C@pobox.com>
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quoth Yadgar:
> But even with this simpler version, a new problem arises: which
> pattern/noise modification to choose to get halfway realistic cloud
> coverage, i. e. cyclonic/anticyclonic whirls? . . .
It would be far from trivial to write but here's an idea. Remember that
a spiral system cannot cross the equator. (I'd qualify that statement,
but this way guarantees that if my assumption is wrong someone will
point out a picture disproving it.)
Consider a crackle function (of standard form) on the equatorial plane.
Within each crackle cell is a spiral function whose strength is
proportional to the crackle function. (This function will add to or
subtract from the cloud cover which is otherwise bozoid.)
Map this plane function stereographically to the globe, by stereographic
projection (through a bit of turbulence) onto each hemisphere.
Disregard it entirely if the crackle cell's core is projected onto land.
Hm. To make the spirals less obviously regular, map a bozo through a
complex function like (1+i)*log(z) ...
--
Anton Sherwood -- br0### [at] p0b0xcom -- http://ogre.nu/
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Yadgar wrote:
>
> Hi Christoph and all others!
>
> Christoph Hormann schrieb:
>
> > Realistic clouds from above are a difficult thing, you should try using warps
> > for local changes of the pattern. A turbulent bozo pattern is often a good
> > start for cloud structures, but you could also try something else.
> >
>
> Warps? Never heard of them... how are they implemented?
> <half an hour later...>
> Ah, I found it in my PoV manual... from browsing through the "Warps" section, it
> looks like the black_hole warp would meet my needs best... but how is the position
> of each warp calculated respective to the actual texture on the object (which might
> be scaled, rotated and translated afterwards)?
>
> Do I have to scale etc. also the warp?
>
you can specify a location and radius, for some other parameters have a look at:
http://www.schunter.etc.tu-bs.de/~chris/etexture.html
(there are no black_hole samples there yet, but i'm working on an extension of
that section)
[...]
>
> Real mountains with an isosurface... you think of wrapping a heightfield around the
> Earth sphere? I'm familiar with tools like DMesh or John Beale's ORB... they work
> pretty well with asteroids, but with a real planet, I'm skeptical... I in fact have
> an 8-bit greyscale heightfield of Earth's land surface on my harddisk, but as its
> scale is still comparatively small (4320 by 2160 pixels) and the mountain ranges
> visible here are in reality hardly higher than 3.000 meters (except for some single
> volcanoes on Kamchatka, on the right limb), I would have to exaggerate the
> heightfield's altitude dimension considerably to see any structures at all!
>
I think the resolution you mentioned is perfectly enough for a first try, if the
height of the mountains is negligible you could also consider a bump_map,
although i don't know how it would look.
[...]
>
> My atmosphere sphere (filled with blue media) in fact reaches 200 km high... but
> when I compare my image to real orbital views, it looks correct to me!
IMO 200 km is far to high and i also remember most real photos having less high
atmosphere.
Christoph
--
Christoph Hormann <chr### [at] gmxde>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/
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From: sacrofts
Subject: Re: Siberian Summer (195K) - realistic cloud swirls?
Date: 2 Oct 2000 19:10:37
Message: <39d915ed@news.povray.org>
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I've just finished the 'view from orbit' picture I've been working on
for the last month. I didn't really use realistic cloud shapes, but
used my camera's vantage point to try and fake some descent clouds using
a marble pattern with a bozo pattern in a pigment_map.
I'll be posting the image on my website when I get a few moments.
http://website.lineone.net/~sacrofts/home.htm
Actually I just finished the image this evening, so give me a day or to
:-)
Below is the code I used for my cloud layers, hope it's of use!
---code
#declare Altocumulus =
texture {
pigment{marble scallop_wave
turbulence 0.8 octaves 9
scale 2000 rotate z*-35 rotate y*-9
pigment_map{
[0.0 bozo turbulence 0.25 scale 0.01 color_map{
[0.0 rgbt 1]
[0.4 rgb 0 ]
[1.0 rgb 0 ]}
]
[0.02 bozo scale 0.01 color_map{
[0.0 rgbt 1]
[0.4 rgb 0 ]
[1.0 rgb 0 ]}
]
[0.2 bozo turbulence 0.5 scale 0.01 color_map{
[0.0 rgbt 1]
[0.7 rgb 0 ]
[1.0 rgb 0 ]}
]
[0.85 rgbt 1]
[1.0 rgbt 1]
}
}
}
#declare Altocumulus2 =
texture {
pigment{marble scallop_wave
turbulence 0.8 octaves 9
scale 2000 rotate z*-35 rotate y*-9
pigment_map{
[0.0 bozo turbulence 0.25 scale 0.009 color_map{
[0.0 rgbt 1]
[0.4 rgb 1 ]
[1.0 rgb 1 ]}
]
[0.02 bozo scale 0.01 color_map{
[0.0 rgbt 1]
[0.4 rgb 1 ]
[1.0 rgb 1 ]}
]
[0.2 bozo turbulence 0.5 scale 0.009 color_map{
[0.0 rgbt 1]
[0.7 rgb 1 ]
[1.0 rgb 1 ]}
]
[0.85 rgbt 1]
[1.0 rgbt 1]
}
}
}
#declare Stratus =
texture{
pigment{ gradient x
pigment_map{
[0.42 color rgbt 1]
[0.45 wrinkles rotate z*45 frequency 25 scale <1,5,1>
color_map{
[0.29 rgbt 1]
[0.3 rgbt <1,1,1,0.2>]
[0.5 rgbt <1,1,1,0.2>]
[0.56 rgbt 1]
[1.0 rgbt 1]} ]
[0.55 wrinkles rotate z*45 frequency 25 scale <1,5,1>
color_map{
[0.29 rgbt 1]
[0.3 rgbt <1,1,1,0.2>]
[0.5 rgbt <1,1,1,0.2>]
[0.56 rgbt 1]
[1.0 rgbt 1]} ]
[0.56 color rgbt 1]}
scale <1000,1000,1000> rotate <0,23,60> turbulence 0.25
octaves 10}
pigment{ granite rotate <-6,-20,0>
color_map{
[0.0 rgbt 1]
[0.2 rgbt 1]
[0.5 rgb 1]
[0.8 rgbt 1]
[1.0 rgbt 1]}
}
}
sphere {0,7977
texture {Stratus}
}
sphere {0, 7969
texture {Altocumulus }
texture {Altocumulus2 rotate x*-0.02 }
}
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