Cumulus Clouds tutorial with trueSKY in Unreal Engine 4

The Simul blog will have many uses, one of which will be helpful tutorials on how to create cloud formations, such as the cumulus cloud, with trueSKY.

For this tutorial, I will be focusing on the most iconic cloud, the cumulus. When you imagine a cloud, most people imagine a big, white, fluffy cloud. That’s what a cumulus cloud is. Their characteristics are a flat base, fluffy appearance and low altitude. To create these clouds, I will be using Unreal Engine 4 with the latest version of trueSKY. Want to follow along? Try trueSKY now for 30 days! You can even follow our guide on installing trueSKY in UE4.

You can presume that for any values I do not talk about, that they have been left at the default value.

Keyframes and Layers

I am going to make a new sequence for this tutorial. So if you are doing the same, make sure you set this sequence as the active sequence in the level, otherwise you wont be able to see your changes.

Firstly, I need to add a cloud keyframe, by right-clicking within the cloud layer and selecting “Add Cloud Keyframe”. If you don’t have a cloud layer, add one by right-clicking in the timeline, then selecting “Add Cloud Layer”. I am also going to set the time to midday, so the sun is shining down on the clouds, allowing me to see their shape easier.

Timeline

Main Settings

The clouds currently look like the default keyframe. For Cumulus, this is too cloudy. So I am going to lower the Cloudiness to 0.54. In Addition to this, cumulus clouds are usually around 2 km in altitude, so I am going to change the Cloudbase to 2.

Next, I am going to take a look at Volume Width. The volume width is how large the repeating areas of clouds is. If you wanted a large number of uniform clouds, you would set this low. Alternatively, if you want large, unique cloud shapes then this value should be increased. For Cumulus clouds, I am going to set Volume Width to 80 km. This will allow for a large amount of smaller clouds, and will not produce clouds that are too large.

To make sure the clouds do not appear to tall, I am going to reduce the Layer Height to 6. Layer height changes the maximum height that the clouds can be produced at. We want our clouds to be thick and vibrant, but not too tall, otherwise we would end up a cumulonimbus style of cloud.

Integration Scheme

Another option I am going to alter is the integration scheme, which can be found in the details panel on the TrueSkySequenceActor. I am going to change the Integration Scheme to Fixed. This changes how trueSKY renders the clouds, instead of using a grid it will use a circular pattern at fixed intervals from the camera.

Changing Integration Method

Using this will give us clouds with more of a fluffy look, as they are not constricted to a grid shape. You can see the clear difference in the image below, where the right image is using the fixed integration scheme. However, the fixed style of ray-tracing can cause artifacts in the clouds when moving quickly, due to the intervals originating from the camera. Fortunately, this will not be an issue for my scene, as I will not be moving or applying wind.

Cumulus Grid vs Fixed

Creating the Cumulus Shape

I want to add extra volume to the clouds, so I am going to set Max Density to 1.2. This will help my clouds have a darker base, as less light will pass through when they are denser.  Furthermore, I am going to set the Base Layer to 0.2. This will help apply some thickness and volume to the clouds, while not making the clouds too large overall.

One way to make the clouds look lighter, and therefore more “fluffy”, is with Diffusivity. So I am going to set the Diffusivity to 0.3. This helps the clouds to appear more transparent, and therefore lighter. Furthermore, I am going to set Upper Density to 0.9 for more thickness in the upper level of my clouds.

I want to adjust the position of the clouds in the sky. To do this I am going to us the World Grid. Firstly, I am going to tick Override Wind, which can be found in the Cloud layer properties. I am now able to move my clouds into the position I desire. To do this I select my cloud keyframe, and within the world grid there is now a blue box, which is the clouds produced by this keyframe. Dragging this around, you will see the clouds move through the scene in real time. I can now position the cloud formation any way I want!

Worley Noise and Scale

Worley Noise is the noise function that trueSKY uses to alter the clouds shape. The Worley settings can drastically change the clouds, so if you’re not careful you will have very unusual cloud formations. All I am going to do is change the Worley Scale to 3.25. When low, Worley scale will produce very large clouds, but few of them. On the other hand, a large Worley scale value will create many small clouds. Therefore, increasing this value slightly will cause my scene to produce just a few more clouds, without losing my desired size.

Blurry Cumulus

Noise

As I am using the Fixed integration scheme, my clouds look almost blurry. This can be fixed by changing the noise surrounding the clouds. The first setting to increase in the Noise section of the keyframe is Sharpness to 0.7. This will have an immediate effect on the quality of the clouds. However, in my opinion this has made the clouds too static, so to add extra noise around the cloud I am going to increase Base Factor to 0.9.

Cumulus finished

And it is done! Here is my example of Cumulus clouds. There are many different settings that could be changed, but then this blog post would go on forever! I encourage you to try out different settings to produce unique and stylish clouds and them share them with the community through our social media or over Slack.

Community Showcase

Our community have also been hard at work on their own projects! One such project is by Marko Barthel, called Across the Seas. Marko is using trueSKY for Unity to create the skies in his world, and he has shared some stunning images with the community.

Half underwaterSunset from boatLarge FOV Sunset

Across the Seas will be a Single and Multiplayer maritime simulation, for all kind of maritime vessels. You can commandeer a huge cruise ship through the ocean, or take to the depths with a submarine! You can check out more about Marko’s projects at virtualtechart.com.

Thank you for taking the time to read our blog. We are currently hard at work redesigning our documentation and fixing bugs, along with new tutorial videos that will be coming soon. If you would like to join our Slack, Contact us or send an email to Contact@simul.co with the email you would like to join with.

Please let us know what you would like us to cover next! We can cover a large range from more tutorials, troubleshooting or upcoming features. The next post will be another brief tutorial on creating a sunset scene.