How to use Chaos Scatter with Corona for 3ds Max - Getting Started

How to use Chaos Scatter with Corona for 3ds Max - Getting Started

• FAQ
• Getting Started (you are here)
• Advanced Features
• Using Chaos Scatter with Other Features of Corona
• Performance and Troubleshooting

Page Contents:

• Getting Started with Chaos Scatter
• Tips and Tricks

Getting Started with Chaos Scatter

This simple guide shows how to use the basics of Chaos Scatter to set up a scene featuring a forest, grass, and rocks on a large surface. 

First, let's get familiar with the basic naming used in Chaos Scatter:

• Distribute-on target object (distribute-on object, target object) - this is the object on which we are scattering other objects. Multiple objects can be used for this as well. 
  
  
• Instanced model object (instanced object, instanced model, model) - this is the object which we are scattering on the distribute-on target object. Multiple objects can be used as well. 

We will start by setting correct units in 3ds Max. It is important to keep the units adequate to the scene scale. For example, if our scene is a forest, it will be extremely uncomfortable to specify object dimensions in millimeters; and if our scene is a macro close-up, it will not make sense to work in meters.
Since we will be rendering a large area, we can set display units to meters:  

To learn more about system units and display units in 3ds Max, see: Setting up your scene in Autodesk knowledge base

We need a base to scatter our objects on. In this example we will use a plane, 500x500 meters large, with enough subdivisions to make it look smooth, and an FFD and Noise modifiers to make its surface uneven: 

We also need some assets for scattering. We will use a tree, a rock, and a grass model: 
Note: you can use Chaos Cosmos, which comes with Corona, to quickly load assets into your scene for free and without having to visit any external services.

Note: pay attention to the pivot of the object that you are scattering! The pivot's position defines the point which will be placed on the distribute-on object and the pivot's Z axis defines the up-axis (upwards along the normals of the distribute-on object). If your trees are flying above the ground - most likely the pivot of the original tree model is placed too low below the tree trunk. Moving the pivot up should fix the issue. 

Once the ground plane and the assets are in place, we can create a Chaos Scatter object anywhere in the scene. You can create it using a button in the dedicated Chaos Scatter toolbar, or go to the 3ds Max Command Panel > Create > Geometry > Chaos > Chaos Scatter:

Once the Chaos Scatter object is in the scene, you can select it and pick:

• The ground object as a "Distribute-on target object"
• The tree model as an "Instanced model object"

Tip: when using the lists of distribute-on target objects and instanced model objects, you easily select those objects, replace them, and perform other operations:

• Right-click on the object name in the list to see a menu with "Select in scene" and "Replace from scene" options:
  
  
  Select in scene - selects the currently highlighted object(s).
  Replace from scene - allows to quickly replace the highlighted object with a different one. 
  
  
• Right-click on the "+" button below the list to clear the list, select the objects from the list, and add the objects from the list to the current scene selection:
  
  
  Clear list - removes all objects from the list. 
  Select objects in scene - selects all objects from the list. 
  Add objects to scene selection - selects the current Chaos Scatter objects and all objects from the list. 
  
  
• Double-click on object names - this will select the object. 

You will immediately see the trees scattered on top of the ground plane in the viewport, and also if you render your scene:

Viewport preview: 

Rendered scene: 

Note: by default, the scattered objects are aligned to the normals of the distribute-on geometry. If you want your scattered objects to always remain vertical (in case of trees your probably want them to be growing straight up, not to lean according to the underlying surface curvature), you can use the "Normal vs. Z" option for this. The value of 0 means that the objects are aligned to the surface normals. The value of 1 means that the objects are aligned to the +Z axis (vertical upwards). The value of -1 means that the objects are aligned to the -Z axis (vertical downwards):  

Tip: if your models turn out to be scattered in an unexpected way (for example with a wrong scale, rotated incorrectly, or placed outside of the distribute-on area), as the first step try resetting the model's XForm in 3ds Max by selecting the model and going to Utilities in the Command Panel and then clicking "Reset XForm": 

At this point, we can see that the trees are not scattered in a very natural way. We can use some of the Chaos Scatter features to improve this. 

First, we can increase the number of the trees using the "Count" value under the Surface Scattering rollout:

To prevent trees from intersecting with each other, we can enable the "Avoid collisions" option under the Scattering rollout:

If the forest becomes too sparse, we can lower the Spacing value under Avoid collisions. The value considers the size of the tree's bounding box, in percent. 100% means that no bounding box can touch each other. More than 100% means that there will be an even larger distance between the trees. Values lower than 100% mean that some overlapping is allowed, but since the tree model does not take all space inside its bounding box, we can go ahead and use values around 30% - 50%. This will make the distances between the trees more natural without visible overlapping:

The forest already looks good, but we can make it even more natural by randomizing the rotation of the trees. We don't want all trees to be growing in exactly the same direction. For this we can use Rotation randomization under the Transformations rollout. We can set:

• X rotation from -5 to 5 (this will slightly lean the trees in the X axis)
• Y rotation from -5 to 5 (this will slightly lean the trees in the Y axis)
• Z rotation from 0 to 360 (this will result in random Z rotation)
  Note: Z randomization is actually enabled by default

Additionally, we can make use of one of Chaos Scatter's most powerful features: the Slope Limitation. This can be used to decide on how steep surface the trees should grow. For example, a very low limit like from 0 to 10 degrees will only allow the trees to grow on almost flat surface. Increasing the limit, for example from 0 to 20 degrees, will let the trees grow on slightly more steep areas. A very high limit, like from 0 to 90 would mean that the trees can grow even perpendicular to the ground, which we probably don't want. 

Another powerful feature of Chaos Scatter is Spline Includes and Excludes, which can be found under the Areas rollout. This can be used to only allow the scattered models to appear inside a specific spline (or a list of splines) or to exclude them from a specific spline area (or a list of splines). Typical uses for spline excludes would be making sure that trees or grass are not growing where a house is placed, or excluding the trees from the area where the camera is placed, to make sure that the camera does not intersect with a tree: 

A circle spline is used as a Spline Include:

The same circle spline is used as a Spline Exclude:

Note: when using the spline includes and excludes option, you can use the additional controls (Near, Far, Scale, Density, Projection axis) to further control the behavior of the instances affected by the spline includes and excludes: 

Remember you can animate Chaos Scatter parameters and objects! This unlocks many possibilities, like growing a forest, making rocks levitate, making certain parts of the scatter disappear, and so on...

Spline includes and excludes can be animated, just like many other features of Chaos Scatter!

Lastly, we can introduce some additional randomization:

We can randomize scale under the Transformations rollout within 25% to 100% range. This means that the scale of the trees will be random, and the smallest allowed models will have 25% size of the original model:

We can also randomize the tree colors a bit by using the Corona Multimap with "Instance" randomization mode enabled. Note that the Multimap and other maps, materials, and Corona features are fully supported by Chaos Scatter. We can plug the original bitmap, which is used to texture the tree leaves, into the Corona Multimap. We can then use it as the only item in the Multimap and use the built-in hue and gamma controls to randomize its colors: 

We can then use similar scattering and randomization techniques to add grass and rocks to our scene. The result is a realistic hill with trees growing on it, accompanied by some grass and rocks scattered on the ground: 

Tips and Tricks

Using the Scatter Lister

In the Chaos Scatter toolbar you will also find the Chaos Scatter Lister tool. It is a great aid when having multiple separate Chaos Scatters in your scene. It can be used to quickly toggle individual scatters on and off and to control their properties such as displayed amount, scattering count and limit, names, and more. 

Controlling Objects on the Lists

When using the lists of distribute-on target objects and instanced model objects, you easily select those objects, replace them, and perform other operations:

• Right-click on the object name in the list to see a menu with "Select in scene" and "Replace from scene" options:
  
  
  Select in scene - selects the currently highlighted object(s).
  Replace from scene - allows to quickly replace the highlighted object with a different one. 
  
  
• Right-click on the "+" button below the list to clear the list, select the objects from the list, and add the objects from the list to the current scene selection:
  
  
  Clear list - removes all objects from the list. 
  Select objects in scene - selects all objects from the list. 
  Add objects to scene selection - selects the current Chaos Scatter objects and all objects from the list. 
  
  
• Double-click on object names - this will select the object. 

Using Chaos Scatter with Chaos Cosmos

Remember that you can use Scatter with Cosmos to:

• Load Scatter presets which are included in Cosmos (either import them into the scene, which will create a whole new Scatter; or select an object and then import a preset - this will treat the selected object as the distribute-on object). 
• Import any Cosmos model into your scene and manually scatter it. 

Chaos Scatter Presets are available in the Cosmos browser ready to assign to a surface or a spline.

How to use Chaos Scatter Presets:

1. Open the Cosmos browser. From the Corona Official Toolbar.
2. You can navigate to the “3D models” category and then click on “Presets” or search for the keyword “Scatter” in the search bar. 
   
   
   
   
3. Find the required preset, then download it.
   
   
   
   
4. Select the preset that you would like to use in your scene and then you can either:
   
   - Import the preset into the scene without having any object selected - this will create a whole new Scatter with a new distribute-on object: 
   
   
   or
   
   - Select an object and then import the preset - this will apply the preset to your currently selected object, treating it as the distribute-on object: 
   
   
   Note: some presets are intended only for surfaces, and other ones - for splines. If you are not sure whether a preset should be applied to a spline or a surface, you can check a visual hint in the preset thumbnail itself (e.g. a blue glowing path suggesting that a preset should be used on a spline), and an additional icon with a tooltip that appears if you hover over it:
   
   
   
5. Then you can modify the settings of your imported preset as you wish!