altit=<val> |
Altitude 90 means sun is at the zenith,
0 means sunset (or sunrise).
Default is 70 degrees.
|
azim=<val> |
Azimuth 0 means sun is behind the observer,
270 (default) sun is in the west.
|
mm=<height> |
Height of the observer above the sea level.
Default is 1.5 metres. The atmosphere ends at 7950 m.
|
view=<z-val> |
Gives the z-coordinate of the observer's viewpoint.
If equal to the height of the observer (default),
then the observer looks horizontal, if view>mm
he looks upwards otherwise downwards.
|
|
The coordinates of the observer are (x=1,y=0,z=mm),
the coordinates of the viewpoint are (x=0,y=0,z=view).
|
angle=<deg> |
Determines the horizontal angular size
of the image. Default is 50 degrees (in analogy to photographic
standard lenses).
|
water |
If this parameter is present, the Earth's surface
is made out of water instead of a pure white desert.
|
waves |
This parameter gives a wave structure to the Earth surface.
|
steamness=<steamness> |
Determines the contamination of the atmosphere with
water vapor. Default is 0.90E-5, which makes a rather
clear atmosphere. More haze may be achieved by values
like 1.32E-5 or 2.39E-5 (very hazy).
|
air=<odepth> |
Transparency of the clear, dry air. Default is 8E-6.
This number determines the intensity of the color
of the sky. If too small, the sky becomes deep blue
or even black, and sunsets don't get very colorful.
If too big, the sky becomes reddish even at midday,
starting with red horizon colors. Natural outlook
of the sky restricts this parameter to an interval
of 4E-6 to 9E-6. The default parameter is nice for
sunsets, but the horizon gets a bit too reddish
at midday.
|
steps=<itwidth> |
Determines the integration step width for the
solution of the radiation transfer equation.
If > 0, its value is taken to be metres
(Warning: The distance from an observer at ground
to clouds of height 8000m seen at the horizon
is about 600km ! Therefore an integration width
of 1m would effect *very* long computation times...).
If < 0, it gives the number of integration points,
independent of the true length of the light path
through some media. Default is -7 (Seven integration
points). This parameter determines the quality
of cloud shadows in the atmosphere (a value too
small may reveil in 'hot spots', since some view
rays hit a cloud, others do not).
|
clouds |
If this option (no value) is present, a layer
of clouds is included in the simulation, the
clouds reside between 2000m and 4000m.
Default is no clouds.
|
sharp=<sharpness> |
Sharpness of the cloud's edges. The bigger this
number, the sharper the clouds. (Internally the
exponent of the density variation.)
Default is 4;
|
scale=(x,y,z) |
Scaling of the clouds. The density variation basically
creates cubic clouds; they should be stretched in
on direction to reveil more realistic outlook.
Default is (0.2,1,1).
|
cmplx=<complexity> |
Sets the factor of fractal turbulance in the cloud
layer. The bigger the complexer, the more
substructures will appear. This factor has big
influence to the computation time, default is 2.
More substructures may also require a shorter
integration width (or more integration points)
(see Csteps parameter below).
|
cdens=<cloud density> |
The maximal density of water vapor in the clouds.
Default is 3E-3 (hardly visible clouds).
It does not make sense to have values smaller than
the steamness factor of the atmosphere. A value
of 1E-2 gives quite acceptable clouds.
|
Csteps=<cloud step> |
Integration width parameter within the cloud layer.
Same rules apply as using the steps parameter of
the clear air.
|
origin=(x,y,z) |
Relative cloud position. This parameter can be used to
put movement on the clouds.
Default is (0,0,0).
|
time=<exposure time> |
Gives the multiplication factor of the computed
intensity before it is used as pixel color. This
parameter is very similar to the exposure time
for photographies. Default is 1.0 (may be called
`seconds' :-) ).
|
ASA=<Film speed> |
Instead of providing an explicit exposure time
the correct exposure time can be determined by
the program itself (performing an `autosensing()').
Nethertheless it is often helpful to give some
additional information how the image should look
like. The resulting brightness can therefore be
corrected by the `ASA' parameter, default is 100.
To darken the effective image to e.g. 75% brightness,
give a film speed of 75. The ASA parameter works
like the true speed of a photographic film in a
camera which does autodetermine the exposure time
for a fixed film speed of 100 ASA.
|