High!

After the disillusioning attempts at building spherical meshes from
heightfields, I tried out Christoph Hormann's Iso_CSG library, which
also contains several iso_hf functions - and it works perfectly, parsing
is no longer a big issue, instead rendering itself is much slower... but
at least, it's interruptible!

Firstly I started with guess what...
...right, Afghanistan of course! This picture shows the country from a
400-kilometres low earth orbit (or LEO, as we space geeks prefer to
say!); the atmosphere is a sphere 50 kms wider than Earth itself, filled
with a repeating media density spherical pattern (the frequency is set
to (Earth_Radius+Atmosphere_Height)/Atmosphere_Height), using also a
color_map
ranging from deep blue to light cyan.

The coulds also are media which fills a thin shell between 4 and 10
kilometres above ground. Provisionally, I used a granite pattern with
turbulence 0.9 and scaled it to 3000 to avoid too small-spaced clouds.

But apart from the fact that many mountains tower above the cloud deck
(because of the low horizontal resolution of the topographical Earth
heightfield - only 10,800 by 5,400 pixels - I exaggerated the relief by
factor 2.5), there are several questions:

1) With granite, I get more or less narrow long bands of clouds, but not
the tell-tale cyclone eddies of the temperate latitudes; also I'm not
able to control the cloud distribution in a way that over deserts you'd
see less clouds or, on the other hand, thick cloud banks at mountainous
western higher-latitude shores like British Columbia, Norway, southern
Chile or New Zealand.
Can this be done with warps - or do I have to model entirely new
functions, perhaps loosely based on models brought up by climate
research?

2) The clouds appear too bright, especially when considering the low
illumination angle in this scene (it's noon at Greenwich, therefore
about 4 o'clock PM (solar time) in Afghanistan). But decreasing the
scattering color value would make them become semi-transparent. Is there
a way to make the clouds darker without losing their opacity?

3) Despite the clouds' thickness being visible at the horizon, the
clouds in the foreground appear flat, without any internal structure.
Can this be changed still with media, or do I have to use isosurfaces?

4) I wonder that the clouds don't cast any shadows, even though I did
not add no_shadow to the clouds' container shell... is this a general
flaw of media?

By the way, the starry sky is a sky_sphere with an object texture; the
star's sizes and coordinates are taken from a popular German sky atlas,
the famous-infamous "Karkoschka"... it's not complete yet, so there are
not many stars visible in this direction.

See you in Khyberspace!

Yadgar

Now playing: Heart of the Sunrise (Yes)

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Attachments:
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Preview of image 'afghanistan_from_leo_bozo_media_clouds.jpg'

news:400EFE3F.9727442A@gmx.de...
> High!
>
> After the disillusioning attempts at building spherical meshes from
> heightfields, I tried out Christoph Hormann's Iso_CSG library, which
> also contains several iso_hf functions - and it works perfectly, parsing
> is no longer a big issue, instead rendering itself is much slower... but
> at least, it's interruptible!
>
> Firstly I started with guess what...
> ...right, Afghanistan of course! This picture shows the country from a
                        ^^^^^^^^^

I like geography very much, so don't take this as an ignorant comment or an
insult... Are you Afghan or what do you find so special about Afghanistan's
topography?


Fernando

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High!

"Fernando G. del Cueto" schrieb:

> I like geography very much, so don't take this as an ignorant comment or an
> insult... Are you Afghan or what do you find so special about Afghanistan's
> topography?

No, I'm not a *real* Afghan... perhaps a virtual one ((:-> - if you take a look
a my earlier postings, you will see that I brought up the Afghanistan issue
several times before, even my very first picture here (October 2000, "Afghan
Sunrise") was an orbital view of Afghanistan rather than the otherwise
inevitable reflective sphere over a checkered plane!

What is so special about Afghanistan when it comes to raytracing? Firstly, it
is a country which elevations range from 280 to almost 7,500 metres, with huge
a variety of terrain shapes, from salt flats in its far west, bizarre buttes
and mesas somewhat more east (New Mexico's landscape has in fact been compared
with Afghan sceneries!), large dune fields, gently rolling loess hills,
dramatic gorges and canyons, fertile basins enclosed by steep mountain ranges
and finally the majestic grandeur of the Hindu Kush with its ice-capped peaks,
many of them never climbed by humans.

Then it is also a land with widely sparse to non-existing vegetation, so that
the bedrock is not blanketed by any soil - truly a geologist's paradise.

But there are deeper reasons for me to deal with Afghanistan... as the whole
story would be too long to tell here, you can read it at
http://home.arcor.de/yadgar/khyberspace/afghan-e.html !

See you in Khyberspace!
Afghanistan Chronicle: http://home.arcor.de/yadgar/index-e.htm

Yadgar

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fcu### [at] yahoocom news:4011b4a6$1@news.povray.org

> Are you Afghan or what do you find so special about Afghanistan's
> topography?

Knowing USA "peace-making" strategy ;) soon it could be rendered as 

difference {
  height_field { ... }
  sphere { 0 Kilometers( 5 )  translate RANDOM() }
}

;)

-- 
#macro g(U,V)(.4*abs(sin(9*sqrt(pow(x-U,2)+pow(y-V,2))))*pow(1-min(1,(sqrt(
pow(x-U,2)+pow(y-V,2))*.3)),2)+.9)#end#macro p(c)#if(c>1)#local l=mod(c,100
);g(2*div(l,10)-8,2*mod(l,10)-8)*p(div(c,100))#else 1#end#end light_source{
y 2}sphere{z*20 9pigment{function{p(26252423)*p(36455644)*p(66656463)}}}//M

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Xns947B935A3B2ACraf256com@203.29.75.35...
> fcu### [at] yahoocom news:4011b4a6$1@news.povray.org
> Knowing USA "peace-making" strategy ;) soon it could be rendered as
>
> difference {
>   height_field { ... }
>   sphere { 0 Kilometers( 5 )  translate RANDOM() }
> }
>
> ;)
>
Hum I think you need a loop here :)

Marc

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