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High!
To make testing easier, I resorted to a simple spherical "test planet"
and tried various camera positions and illumination angles with all five
scattering types (and yes, it wasn't media but the isosurface which
slowed down my renderings - now each scene took about 70 seconds!).
The simplified test planet is a sphere with a radius of 5,100 POV units
(1 unit equals 1 kilometre); the media is contained by a sphere with a
radius of 5,150 units. In all scenes, the illumnating star is a simple
point light; in all ground scenes (all scenes from row 3 on), the camera
is placed 0.0017 units above the planet's surface.
Method, samples and intervals settings are default (see code attached here).
The most striking flaw with all scattering types is the extremely dark
sky at low illumination angles - the sunrise looks like on Mars but not
like on a planet with Earth-like atmospheric pressure. Could using an
area light instead of a point light be helpful here? Or do I have to
fake the indirectly illuminated sky before dawn by using an additional
(shadowless) fill light source?
Reactor's suggestion of adding an absorbing component did not work at
all - regardless which ratios between scattering and absorbing, the sky
turned even darker!
Then, at medium illumination angels (~45 degrees), the otherwise pretty
realistic sky with scattering type 1 and 4 still turns too greenish
close to the horizon...
See you in Khyberspace!
Yadgar
// Planetary Surface Camera test scene
#declare Model_Planet=
sphere
{
0, 1
texture
{
pigment
{
bozo
color_map
{
[0 rgb <0, 0, 0.2>]
[0.5 rgb <0, 0.4, 1>]
[0.5 rgb <0.2, 1, 0>]
[0.65 rgb <0.2, 1, 0>]
[0.67 rgb <0, 0.6, 0.2>]
[0.78 rgb <0, 0.6, 0.2>]
[0.79 rgb <0.5, 1, 0.5>]
[0.86 rgb 0.6]
[0.92 rgb 0.6]
[0.925 rgb 1]
}
turbulence 2
octaves 7
omega 0.2
}
finish { ambient 0.1 diffuse 1 brilliance 0.5 }
}
scale 5140
}
#declare Atmosphere =
sphere
{
0, 5190
hollow
material
{
texture
{
pigment
{
color rgbt 1
}
}
interior
{
media
{
#declare tp=int(clock/13);
scattering
{
tp, <0.8, 0.8, 1>/80
#if (tp=5)
eccentricity 0.3
#end
}
density
{
spherical
density_map
{
[0 rgb <0.25, 0.5, 1>]
[0.005 rgb <0.25, 0.5, 1>]
[0.011 rgb <0.9, 1, 1>]
[1 rgb <0.9, 1, 1>]
}
}
}
}
}
}
object { Model_Planet }
object { Atmosphere }
light_source
{
<1000000, 0, 0>
color rgb 1
looks_like
{
sphere
{
<1000000, 0, 0>, 25000
texture
{
pigment { color rgb <1, 1, 0.65> }
finish { ambient 1 diffuse 0 }
}
}
}
}
// #declare view=4;
#switch (mod(clock, 13))
#case (0) // global view, centered on terminator
#declare lat=0;
#declare long=180;
#declare ht=20000;
#declare dir=0;
#declare azi=-89.9999;
#break
#case (1) // global view, centered on substellar point
#declare lat=0;
#declare long=270;
#declare ht=20000;
#declare dir=0;
#declare azi=-89.9999;
#break
#case (2) // substellar point from 1.7 metres, looking north
#declare lat=0;
#declare long=270;
#declare ht=0.0017;
#declare dir=0;
#declare azi=0;
#break
#case (3) // Star from substellar point at 1.7 metres
#declare lat=0;
#declare long=270;
#declare ht=0.0017;
#declare dir=0;
#declare azi=89.9999;
#break
#case (4) // 45 degress west of substellar point from 1.7 metres,
looking north
#declare lat=0;
#declare long=225;
#declare ht=0.0017;
#declare dir=0;
#declare azi=0;
#break
#case (5) // Star from 45 degrees west of substellar point at 1.7 metres
#declare lat=0;
#declare long=225;
#declare ht=0.0017;
#declare dir=90;
#declare azi=45;
#break
#case (6) // Zenith from 45 degrees west of substellar point at 1.7
metres
#declare lat=0;
#declare long=225;
#declare ht=0.0017;
#declare dir=90;
#declare azi=89.9999;
#break
#case (7) // 70 degress west of substellar point from 1.7 metres,
looking north
#declare lat=0;
#declare long=200;
#declare ht=0.0017;
#declare dir=0;
#declare azi=0;
#break
#case (8) // Star from 70 degrees west of substellar point at 1.7 metres
#declare lat=0;
#declare long=200;
#declare ht=0.0017;
#declare dir=90;
#declare azi=20;
#break
#case (9) // Zenith from 70 degrees west of substellar point at 1.7
metres
#declare lat=0;
#declare long=200;
#declare ht=0.0017;
#declare dir=90;
#declare azi=89.9999;
#break
#case (10) // 90 degress west of substellar point from 1.7 metres,
looking north
#declare lat=0;
#declare long=180;
#declare ht=0.0017;
#declare dir=0;
#declare azi=0;
#break
#case (11) // Star from 90 degrees west of substellar point at 1.7 metres
#declare lat=0;
#declare long=180;
#declare ht=0.0017;
#declare dir=90;
#declare azi=0;
#break
#case (12) // Zenith from 90 degrees west of substellar point at 1.7
metres
#declare lat=0;
#declare long=180;
#declare ht=0.0017;
#declare dir=90;
#declare azi=89.9999;
#break
#end
#declare surfPos = trace(Model_Planet, 0,
<sin(radians(-long))*cos(radians(lat)), sin(radians(lat)),
cos(radians(-long))*cos(radians(lat))>);
#declare camPos = surfPos + vnormalize(surfPos)*ht;
#declare dirVect = <sin(radians(dir))*cos(radians(azi)),
sin(radians(azi)), cos(radians(dir))*cos(radians(azi))>;
camera
{
sky surfPos
location camPos
look_at camPos + vrotate(dirVect, <lat-90, -(long-180), 0>)
angle 40
}
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