Procedural Biomes , Unreal & Houdini

I developed this HDA for my latest game Land of Hatti. Since manually designing maps for open-world would require an immense amount of time I decided to use a procedural approach for map generation and instancing.

A- Biome Map Generation

1. Height Map Generation
   • A procedural height map is created using Perlin noise (pnoise).
   • This serves as the foundation for determining elevation, including mountains, plains, and valleys.
2. Water Map Creation
   • Three types of water bodies are generated:
     • Sea: Surrounding land tiles.
     • Rivers: Flowing from high-altitude (high precipitation) areas to the sea, following downward slopes.
     • Lakes: Formed in specific conditions such as:
       • High precipitation regions.
       • Volcanic activity on mountain peaks.
       • Crater depressions.
       • Aeolian (wind-formed) basins.
3. Humidity Calculation
   • Humidity is determined based on:
     • Levels of precipitation.
     • Proximity to water bodies.
4. Temperature Calculation
   • Temperature is computed using factors like:
     • Latitude: North-South location on the map.
     • Distance to Water: Coastal areas are generally cooler.
     • Elevation: Higher altitudes have lower temperatures.

After Temperature and humidity paremeters are calculated, biomes are selected by cross-referencing the a predefined matrix (as illustrated in the image below). This process creates a dynamic and realistic biome map that reflects the natural diversity of ecosystems

B – INSTANCING ASSETS

Once the biome map is assigned, the scattering process begins. This involves placing various assets like trees, grasses, and rocks across the map in a structured, multi-step process.

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Scattering Process

1. Primary Pass
   • Larger, primary objects such as trees and big bushes are scattered first.
2. Secondary Pass
   • Secondary objects, like grasses, tree-connected elements (e.g., ivy, roots), and flowers, are added in this step.
3. Final Pass
   • Non-biome-specific objects like rocks, sticks, and debris are scattered.
   • Factors such as scatter density, proximity to water, spacing between objects, and occlusions by larger objects are considered to ensure a natural arrangement.

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C-EXPORTING WITH UNREAL ENGINE

Scattered assets are exported to Unreal Engine as points with instance data. Each point contains the following information:

• s@unreal_instance
  • Specifies which object to instance, using the full reference directory of the asset in Unreal.
• s@unreal_uproperty_CollisionProfileName
  • Defines the collision profile, such as "BlockAll" or "NoCollision".
• i@unreal_num_custom_floats
  • Indicates the number of custom data channels.
  • In this case, 4 channels are used:
    • The first three represent the base color of the object.
    • The fourth channel determines whether the material should use the object’s vertex color or the point color.

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Organizing Assets

To maintain consistency, the same asset structure is used in both Houdini and Unreal. The structure follows a logical hierarchy:
Root → Trunk → Branch → Twig → Leaf → Variant.

For example, scattering a bush geometry adheres to this organized structure, as shown in the accompanying image.

This approach ensures efficient asset management and a seamless workflow between Houdini and Unreal Engine.

• REF: https://en.wikipedia.org/wiki/Biome#/media/File:Climate_influence_on_terrestrial_biome.svg