World Machine Tip of the Month : Sunday, August 25th, 2002.

#3: Cascading Terraces

Something that is easily noticable when looking at river canyons and other terrain features that have been carved by water over the years is not just the presence of terraces, but rather the fact that there exist several scales of terraces, as the cycle of the river cut at different depths over the years. Sometimes the terraces are also partially obliterated by the ravages of time.

This tutorial shows how to demonstrate a similar effect. This is an advanced tutorial, simply because the graph is somewhat intimidating at first look.


Here is the device graph for this effect. Intimidating at first sight, it actually is very simple. I'll break it down into the component parts below:





Terrain Creation
The first step is to create a suitable base terrain for the terracing to act upon. Here it is a relatively simple setup, with a single perlin noise generator set to height-based multifractal mode. A transform is added directly after it to shape the terrain.


Terracing
This is the fun part. Each terrace device you see here is set to produce a different number of terraces, which corresponds directly to the size of the terrace. The output of the first is connected to the main input of the second, and so on.

What makes things interesting, however, is that each terrace is set to only effect certain parts of the terrain. The major terraces span all but the tallest part of the terrain, while the middling-sized and small terraces exist in different bands in the middle.

The other thing to note is that the height selection that determines the range in which the terrace exists is multiplied by perlin noise generators (which are not shown in this picture). This way, the terrace of that particular size doesn't appear everywhere.



Erosion
The last group of devices have to do with erosion. The goal was to have the terraces be obliterated by the soil movements in some spots, while in others they remain intact. The output of a perlin noise generator is used to choose between the terraced terrain, and a heavily eroded version of it. This causes the desired effect.


Lastly, the world was built at a size of 1024 and rendered in Terragen to produce the scene you see at the top. The TMD file is available here, although be aware that it differs randomly from the terrain that was rendered. Here's a 3/4 view of the terrain produced:


Tutorial by Stephen Schmitt. 8/25/2002.