Erosion is a time-based geological function that modifies terrain by breaking and/or moving rocks, dirt and sediment typically from higher altitudes to lower altitudes.
Real world erosion is a combination of a number of functions including hydraulic (rain), thermal, fluid flow such as rivers, and wind.
TerreSculptor supports a number of varied erosion functions, including Hydraulic, Flow, Slope, and Thermal, and the next version should include Velocity. Future version "wish list" items include time-varying fractal rain fields and terrain soil hardness based on altitude/slope or an imported mask.
Over the next few blog posts we will have a quick look at the variety of available erosion functions in TerreSculptor.
Hydraulic (Rain) Erosion.
Hydraulic erosion is a close neighbor of fluid flow erosion, with the main difference that it is based on global water coverage at a single unit scale, and typically does not consider the terrain's water flow map or large water flow velocity fields (ie. streams and rivers etc.).
In simpler terms, hydraulic erosion simulates constant even rain over the entire terrain and erodes with sediment movement down slopes on a per-pixel level. Computer simulated erosion of this type is a form of cellular automata.
The hydraulic erosion function in TerreSculptor is based on the research of Musgrave, Kolb and Mace. It extends their research to include support for adiabatics and variable evaporation. It also uses the full Moore cell neighbor technique to provide a more accurate simulation, but at the cost of longer computational time.
The erosion dialog provides full access to all erosive properties, such as how often it rains and how heavy the rainfall is, and includes the option of saving any auto-generated masks for use as weightmaps on the terrain within the video game engine. These weightmaps are typically used to provide accurate and natural-looking terrain texture mapping along areas of greater water and sediment flow caused by the erosion.
The results of hydraulic erosion typically move dirt from higher altitudes to lower altitudes through sedimentary suspension in rain water. Visually it essentially fills fine holes and pushes the sediment down slopes. With extreme time durations in the order of simulated billions of years, TerreSculptor's hydraulic erosion will change mountains into plains.
The erosion dialog:
The 3601x3601 DEM terrain file we are going to erode:
After erosion:
And an animated flip between the original and eroded terrain:
Finally, the auto-generated water flow mask that can be used as a terrain weightmap, resampled from its original 3601x3601 size:
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