By Andrew Morgan (Aegisprime) (194.117.133.118) on Friday, November 01, 2002 - 07:15 am:

No, it’s not another $20 book, it’s a free tutorial on how to create nice skies with your favourite 3D software - Yay!



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…”

SkyTracer 2 promises a lot but isn’t very well documented and even Dan Ablan skips over it in Inside LightWave 7. I spent a day tinkering with SkyTracer to see exactly how it works and thought I’d share my findings with the LightWave community.

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 you 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 you 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 settings to the same as the panels 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 – Andy.

By brett anderson (Brett_Anderson) (203.198.24.4) on Friday, November 01, 2002 - 10:11 am:

hi Andy
i wanna ask if i want to render an animation about sun rise to sun set, as well as the moving of the cloud
how can i do it with skytracer2?

thanks a lot

By ingo (Ingo) (62.109.114.252) on Friday, November 01, 2002 - 10:21 am:

Thanks for the great tutorial for ST2, just one additional note: Don't save the SkyBaker maps in just 32Bit PSD files, use the full 128Bit option and tweak the skies in Imageviewer.

ingo

By Andrew Morgan (Aegisprime) (194.117.133.118) on Friday, November 01, 2002 - 11:39 am:

Brett: Animating your sunlight source will correctly shade the clouds - you'll even get a "red shift" when the sun touches the horizon.

To animate the clouds simply set up an envelope to move their position in whatever direction you want - for instance go to the texture editor, select your STClouds procedural and set up a position envelope mith say .5m at frame 50 in the +X axis. Make sure your pre and post behaviour is linear and then copy the settings to the second procedural (turbulence in my tutorial) - your clouds should now drift from left to right across the sky. If you make the turbulence procedural move slightly slower they'll change shape too!

Ingo: Good point about saving as 128bit - makes tinkering with them later a lot easier!

By Andrew Morgan (Aegisprime) (194.117.133.118) on Friday, November 01, 2002 - 11:48 am:

Here's a little example (hope this works)

By william greenlee (Billyboy) (12.218.128.69) on Friday, November 01, 2002 - 08:13 pm:

Cool stuff gentlemen!
Very cool stuff!

By John Pattullo (Shootme) (172.181.228.199) on Saturday, November 02, 2002 - 06:49 am:

is there any way to amke sky tracer produce alien skys? so i can makes a green sky or a red martian sku?

By Andrew Morgan (Aegisprime) (194.117.133.118) on Saturday, November 02, 2002 - 07:23 am:

Not from within SkyTracer but here's a little oddity I just discovered - If you turn all the "Atmosphere" settings down (Atmosphere: 1km, 0%, 0%, 0% Haze: 0m, 0%, 0%, 0%) then you'll get a black and white sky which you could use in LightWave as an Alpha map to make the clouds any colour you want against any background you want.

Here's a quick 'n dirty test I lashed up using a gradient, a cloud image as an Alpha and LightWave's compositing:



Keep those questions coming! ;-)

By ingo (Ingo) (213.39.144.160) on Saturday, November 02, 2002 - 09:03 am:

Another nice idea is to use the colorshift feature for the sun, nice psychadelic things when you switch it to -150 % or other strange inputs.

ingo

By Andrew Morgan (Aegisprime) (194.117.133.118) on Sunday, November 03, 2002 - 05:59 am:

One thing I did forget to point out is that changing the intensity and colour of your light source will obviously change the look of the clouds too.

By riki (Suture) (203.109.249.131) on Saturday, December 28, 2002 - 04:49 am:

Nice work guys