Erosion

Strength and Rock Softness

Both Strength and Rock Softness parameters affect the aggressiveness of erosion, and effect from increasing of one can be similar to the effect of increasing other, but there is still the difference, derived from the definition of these parameters.

Lesser strength means dissolved soil will be dropped earlier because of lower water transport capacity, and lesser softness means that the rock will be eroded slower but dissolved sediment will be dropped farther. This results in different distribution of deposits, gullies, and shapes of erosion features.

Downcutting

Downcutting effectively transports sediment far away from its origin. If shorter transport distance is desired, for example, for faster alternating between erosion/deposition, set this parameter to 0.0, or set Inhibition to higher values.

Scale and Feature Size

The size of the "features" created during the erosion process - namely the width of largest valleys and ridges between them - is controlled by the Feature Scale option is where you can achieve artistic control over the erosion process.

The Real Scale option automatically controls the general scale (the extents of the terrain and the vertical scale), using the scale set in the Terrain Definition. Although it can be turned off to manually change the 'physics' of the erosion system, although it is not recommended for most scenarios.

When using Parallel Processing, the erosion algorithm can become non-deterministic. This means while most of the major flows will appear in the same location, smaller features may appear somewhat different every time the node is processed. To ensure fully deterministic processing, disable Parallel Processing. This will sacrifice processing speed to ensure your results are consistent.

Sediment Removal

The new Sediment Removal feature lets you remove sediment deposits generated by the erosion process. By default, the property applies uniformly across the entire terrain, but it can be driven by a heightfield or mask.

-- Needs image --

Processing Mask

You can use two forms of masking for the Selective Processing: the built-in masks called Bias Types, or a custom mask provided via the Area input. Custom masks can be any heightfield.

The built-in bias masks are Slope and Altitude. They are mainly provided for convenience so you can quickly apply Selective Processing and be able to use it frequently without creating several nodes. Both aspects go from 0 to maximum in a normalized scale. This means 0% is the bottom, while 100% the top. For example, if you want to mask the last 10% of a mountain peak, you would use 90% for the Altitude bias. You can invert the mask by enabling Reverse.

The bias mask modulates, or drives, the value of the parameter across the terrain region. For example, if you provide a Rock Softness mask while your Rock Softness parameter is set to 35%, it will map the black or 0 part to 0% while the white will map to 35%. Similarly, Erosion Strength maps to the Strength slider, and Precipitation Amount maps to the Duration slider.

Data Output

The Erosion and Wizard nodes create three key data outputs:

These maps can be used for texturing, or for driving other nodes.

Like other data maps, the output may not be readily visible to the human eye. You can use Fx to autolevel or equalize the output. You can also use Abs to create a solid mask.

In digital terrains, inexperienced artists will often try to use the Flow output too prominently for texturing. While this may work in some situations, it tends to create unrealistic textures and can make your terrain look fake and "CG". See the Misconceptions section below.

Determinstic Output

It is worth noting that due to the nature of the algorithm and parallel processing, the erosion flow may differ slightly each time. To ensure 100% exact results every time, you can turn on the Deterministic option in the Erosion node. This will force Gaea to use a single processor core which will result in slower processing, but will ensure your results are completely predictable.

This may not always be necessary. There are also workarounds. For example, if you wish to control certain major flow lines, you can create a mask for the starting points of those flows and feed it to Selective Processing. This is usually best done in a second Erosion node, while the first one provides general erosion across the terrain.

Further Reading

See Eroding Terrains for general information on erosion, how it applies to procedural terrains, and misconceptions about erosion.

See these tutorials for examples of practical usage:

• Selective Erosion
• Multipass Erosion