OK, so there I am, working
on a shot that needs a very specific type of
sky – looking through my collection of
images I don’t find anything I can use
for this one “I know” thinks I, “I’ll
use SkyTracer – how hard can it be…” Before
you get started, make sure you know your way
around LightWave surface editor. Ready? Alrighty
then!

Load up LightWave, pick the
scene tab then click on Tools/SkyTracer and enable
VIPER. By default you’ll have a dull blue-to-brown
gradient. The “Dissolve” setting
dissolves your sky in and out of your scene and
the Planet Radius is set to the same radius as
Earth – you shouldn’t need to change
it. SkyBaker lets you bake your skyscape into
image files – we’ll return to that
later. Let’s look at the SkyTracer Atmosphere
panels:



The atmosphere & haze controls
light scattering in SkyTracer. With these panels
you can adjust the thickness of the effect, the
luminosity, opacity & falloff. For most scenes
you can leave these at their default settings – if
you want to test them out to see what different
looks you can get do so AFTER you’ve got
your clouds looking how you want. Adjusting the
quality increases render times but improves the
effect of light diffusion. Medium seems a good
compromise between quality and render times – see
the examples below:



Let’s move onto the “Clouds” tab – this
is where thing get interesting! Select the “Low
Altitude Clouds” and click on enable clouds – you’ll
see some fairly uninspiring, blobby clouds appear
in the VIPER preview. By default SkyTracer uses
the Turbulence procedural texture to create its
clouds – click on the “Texture” button
and select Procedural type “STClouds” then
change the texture axis to Y. VIPER should be
displaying a thick, uniform layer of cloud. Let’s
look at the texturing option for STClouds:



Much of this should be familiar
to you – the most important settings are
Lacunarity, Octaves and Cloud Type. Lacunarity
adjusts the turbulence of the clouds – a
setting of 1 creates featureless blobby clouds,
higher settings introduce more disturbance but
a setting of 5 or more starts to add repetitive
patterns into the clouds, for now just leave
it at its default setting of 2.0. Octaves change
the fractal detail of the clouds – higher
settings increase detail but impact render times.
Leave the Octaves at their default setting of
6.0. Cloud Type allows you to change the procedural
template for the clouds – cumulus and cirrus
clouds plus jet trails are available. Leave it
set to cumulus for now.

Change the Texture Value to
100% and adjust the Scale to 1m x 1m x 1m. We
could close the texture editor now and start
making changes using the clouds tab but I find
you have a bit more control if you add an extra
texture layer. Add a procedural layer (it should
default to Turbulence) and change the blending
mode to “Subtractive”. Your huge
bank of clouds should change to a few wispy ones
in the distance. Set the Texture Value to 100%,
the contrast to 50% and the scale to 2m x 2m
x 2m – now you can adjust the density of
your clouds by changing the layer opacity – play
around with the opacity settings to see what
happens before setting it to 40% and closing
the texture editor.



Back on the clouds tab, change
the “Low Altitude Clouds” settings
to the same as the picture above. Most of these
controls seem to work together so this part can
take a lot of tweaking. Density controls how
much “moisture” the clouds contain – higher
settings make them darker and allow less light
to diffuse through them. Opacity has a similar
effect – experiment with them to see the
differences and similarities. Luminosity enhances
the effect of light diffusing through the clouds – a
50% setting seems to work well. Contrast helps
define the overall shape of the clouds - high
settings between 300% and 500% seem to work well.
Volumetric Rendering allows LightWave to render
your clouds with volume in a similar fashion
to HyperVoxels – turning this off makes
SkyTracer 2 behave like the original SkyTracer.
Make sure Texture shadows is on or you wont see
the shading on the underside of your clouds.

Go to the “High Altitude
Clouds” and enable the clouds to create
a wispy secondary layer – leave the settings
at their defaults and leave volumetric rendering
off for this second layer.

The clouds look a little too “busy” around
the horizon so go back into the STClouds texture
settings for the low altitude clouds and set
the Z axis falloff to 4%. Exit the texture settings
and go back to the Atmosphere tab – change
the quality to “Medium” then press
F9 and do a test render – this should take
under a minute at 640 x 480 on a fast CPU. It
should look something like this:



Don’t forget you can
change the density of the cloud layer by adjusting
the layer opacity of your Turbulence layer in
the texture editor. When you have some settings
you like, make sure you create a preset for them
using VIPER’s “Add Preset” button.

Once you’re finish tinkering
with your clouds you can use SkyBaker to bake
them into an image file(s) – you have the
choice of a cube, sphere, cylinder or a lightprobe
image for use with LightWave’s ImageWorld
plugin. Generally, rendering with SkyTracer is
quite slow so it’s better to use SkyBaker
but you’ll have to render the images at
around 4 times your scene’s resolution
in order to avoid blurring – i.e if you’re
rendering at 720 x 576 your SkyTracer maps need
to be 2880 x 2880 – this can take a while
(probably best to leave it overnight) but you
can always adjust the colours/contrast/saturation
in Photoshop/Aura later to use them in a number
of scenes. One other point – if you’re
baking your images DON’T use antialiasing – they
don’t really need it and it increases the
render time massively – you’ve been
warned!

Good luck and have fun playing
with SkyTracer 2!

Feel free to email me if you
have any questions – [Tens de ter uma conta e sessão iniciada para poderes visualizar este link]]