This beginner level tutorial is an introduction on making nice and interesting skies for Terragen 2.

While the node based network might seem intimidating for new users in the first place, it can actually be quickly understood. We are going to showcase atmosphere and clouds work in Terragen 2 by creating an interesting sky with our step by step guide.

Prerequisites:

Please read the "User Interface Overview" hosted at http://forums.planetside.co.uk/index.php?topic=6

We also work with the default project. That is the scene that appears when you start Terragen 2. Furthermore, we assume you are familiar with moving the camera around in Terragen 2.

Step 1: Move Camera to new point of view and add a 3D cloud layer

Open Terragen 2 and move the camera near the ground and look upwards a little, so that 20% of the camera view are terrain, the rest is sky. Plan blue sky, for the moment, but we are going to change that. For a start, it would be good to keep the current camera heading, so that the sun shines from ~9 o'clock (sun from front and left, sun disc must not be visible in the 3D preview window.

Now we click on the button labeled "Atmosphere". Once we clicked that, a button, just below the open and save icon appears, labeled "Add cloud layer". We choose the "Low Cumulus 3D" flavour. Your 3D preview should now show a sky full of clouds.

Step 2: Blending out clouds near our camera location

You may have noticed that the node network has been extended with a cloud layer node and a density fractal node. Think of the cloud layer node to be what it says - a cloud layer that exists at a certain height. The density fractal node tells the cloud layer where exactly the clouds will be rendered in the sky. The density shader "draws" a greyscale map for the cloud layer. White says "here you're going to put a cloud", black says "Here you are not going to put a cloud". Any shade of grey tells the cloud layer how thick the cloud will be at this point.

Now, the denstiy fractal is infinite in its range, so the cloud layer is everywhere around the entire planet. For our still scene, we want to render clouds a little farther away from the camera, and leave a little bit of blue sky within a radius directly above us. The distance shader can help us do this. When we add a distance shader, we are going to have the following "chain of command".

1. Distance shader telling the density fractal shader: "anywhere starting from X meter away from the camera, to infinity, you can draw your greyscale map"
2. Density fractal shader goes: "ok, I draw instruction on where to put clouds now in the area the distance shaders tells me it's ok."
3. Cloud Layer goes "Ok, so according to this map from the denstiy shader, I'll put a cloud here, another one there and...."

In order for the distance shader to have an influence on the cloud's density fractal, we must tell the density fractal that is has a so called "blendshader". Double click on the density fractal node and a dialog window will open. Check the box labeled "blend by shader" and then click on the little button next to that labeled with the three dots "...". Then a little window pop up for options. You select "create new shader", "color shader", then "distance shader". Voila, your node network now has a distance shader attached to the blendin shader input port of the density fractal.

Double click on the distance shader node now. In the upcoming dialog, enter 3500 in the input box for "near distance". Then, enter 4000 for "far distance". Now look at this, your 3D preview window will update immediatly, and all clouds near the camera are gone! Look at the distance shader dialog again. It says far color is white, and near color is black. "Near" is defined as anything up to 3500 meter, and White is defines as anything 4000m away or beyond. In between 3500 and 4000 is a grey zone, so that the border for "clouds or no clouds" is not too sharp. It's as easy as this.

Step 3: Influencing the shape and apperance of our clouds.

For the sake of this Terragen 2 tutorial, let's say we'll want nice saturated cumulus clouds. These clouds are taller than average, so we need to tell Terragen 2 to make them thicker in the first place, to give them some room. Open up the dialog for the cloud layer, and enter 2000 in the field labeled "cloud depth". Ok, that made the layer notably thicker. We also want the clouds to be a little broader. So need to tell the density fractal that it should draw broader clouds. Open up the dialog for the density fractal and enter 1500 into "feature scale". The feature scale is the most dominant size. So now, not clouds will be 1500 wide, and (up to) 2000m tall. However, these clouds can "clump" together and make broader clusters of clouds. That's defined by the factor "Lead-in scale", but we'll leave that at the default value for now.

We still want the clouds to become taller, more separated out and of course, if you had a close look, have billowry shapes. Because of this, we take a few more steps. We'll have to bring down the height by which Terragen 2 will begin to render clouds *within the already defined layer*. For that we:

1. Go to the "tweaks" tab in the cloud layer node. Decrease Coverage Gamma by half and check "flatter base". Decreasing the Coverage Gamma also reduces the overall coverage, and we have to make up for that in the next step. Soft base and Base Wispiness also bring down the bottom of the clouds, hence influence the overall shape. You can play with those two settings later and see what effect they have.
2. Open the cloud density fractal dialog, go to the density tab and increase the coerage adjust value from 0 to ~0.1
3. In the "main" tab, we increase the cloud density. A value of 0.03 should do fine. Enter 10 for edge sharpness.

Fine. Now our clouds are looking like saturated cumulus clouds. Unfortunately, a render will reveal a lot of grain in the atmosphere. This happens when Terragen 2 doesn't take enough samples of the atmosphere and/or clouds to accomodate for high contrasts (e.g. bright sky next to dark parts of clouds). We take the following 2 measures to fix this:

1. Open the atmosphere dialog, switch to the quality tab. Then we increae the number of atmosphere samples to 32.
2. Open the cloud layer, go to the quality tab. Increase the quality slider all the way to the right. We want quality = 1.
3. In the same tab, we also set the acceleration cache to "none (highest quality), or "conservative acceleration". The higher the settings here, the longer the rendering process will last. Ususally, for high contract clouds like cumulus clouds, the final render quality justifies the longer render times.

The Result:

After a few level adjustments this is what we've got.

You may download our example project file here and use that as a base for further experimentation. That being said, we only scratched the surface of Terragen's capabilities with clouds and the atmosphere. There's still a whole lot to learn, which we may cover in follow-up tutorials. Happy rendering :-)