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#declare Pedantic=true;
It is really not necessary to use a special shape to model an entire
planet. Earth's tallest mountain (Mt. Everest) is 8848 meters high; the
radius of the Earth is about 6366 kilometers. On an 800x600 image
depicting the entire planet, situated such that Everest was on the very
edge of the disk, the height of the mountain would be about
300*8848/6000000 = roughly .41 pixels. Anti-aliasing will turn this
into a bit of fuzz at the edge of the disk.
To get the shadows of mountains, use a normal pattern in the texture.
#declare Pedantic=false;
Sorry, couldn't help myself.
Regards,
John
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No prob. I was trying to get a fractal-looking edge to thr continents.
BTW: you mean those 30 cm globes from elementary school with 2 mm mountain
range bumps on them are exaggerated!?!
John VanSickle wrote:
> #declare Pedantic=true;
>
> It is really not necessary to use a special shape to model an entire
> planet. Earth's tallest mountain (Mt. Everest) is 8848 meters high; the
> radius of the Earth is about 6366 kilometers. On an 800x600 image
> depicting the entire planet, situated such that Everest was on the very
> edge of the disk, the height of the mountain would be about
> 300*8848/6000000 = roughly .41 pixels. Anti-aliasing will turn this
> into a bit of fuzz at the edge of the disk.
>
> To get the shadows of mountains, use a normal pattern in the texture.
>
> #declare Pedantic=false;
>
> Sorry, couldn't help myself.
>
> Regards,
> John
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Wasn't it John VanSickle who wrote:
>#declare Pedantic=true;
>
>It is really not necessary to use a special shape to model an entire
>planet. Earth's tallest mountain (Mt. Everest) is 8848 meters high; the
>radius of the Earth is about 6366 kilometers. On an 800x600 image
>depicting the entire planet, situated such that Everest was on the very
>edge of the disk, the height of the mountain would be about
>300*8848/6000000 = roughly .41 pixels. Anti-aliasing will turn this
>into a bit of fuzz at the edge of the disk.
>
>To get the shadows of mountains, use a normal pattern in the texture.
However, if you attempt to render the Moon with only a normal pattern
you'll get a result that shows a clearly unrealistic terminator line.
The tip of a mountain on the equator that's half a pixel high will still
be in sunlight when it's 4 degrees (acos(800/800.5)), past the
terminator. That's a clearly visible 18 pixels. Normals don't cope with
this effect, and plunges the mountain into darkness exactly at the
terminator.
E.g. in this example, which admittedly has mountains a little higher to
exaggerate the effect, exactly half of the moon is illuminated, and
you'll see a very artificial looking straight shadow line.
camera { location <0, 0, -2.5> look_at <0, 0, 0>}
light_source {<-1000,0,-0> colour rgb 1}
sphere {<0,0,0> 1 pigment {rgb 0.9}
normal {granite
scale 0.5
slope_map{
[0 <1,1>]
[1 <0,0>]
}
}
}
>#declare Pedantic=false;
--
Mike Williams + #
Gentleman of Leisure
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