Wednesday, October 19, 2016

Banding together

I've been implementing the wind and rainfall model for the tectonic-based terrain generation program, and found that it had developed bands.  This is based upon the algorithm described by Soon Tee Teoh in "River and Coastal Action in Automatic Terrain Generation."  Alas, as implemented by mean it is leading to bands of absolutely arid land (white portion at left) interspersed with bands of average rainfall.  I suspect the problem lies with my implementation, not in the algorithm as described.

Rainfall from moisture carried on winds from the east
The more intensely blue portions in the image above indicate a higher amount of rainfall in those cells.  This is the result of a simple algorithm to emulate orographic rain.  You can see corresponding mountain range in the terrain image below.  What seems to be happening is that the wind is pushing moisture westward over the mountains, during which the higher peaks result in more rain at those points and less to the west.  In some cases, the amount of rain was sufficient that the rain "runs out" a bit west of the mountains.  Where the wind pushed over lower portions of the mountain range, enough moisture was left that it "rained" all the way across the continent.

In essence, I'm getting a banded, displaced rain shadow effect.  That's not all bad.  The banding definitely needs to be resolved, whether through tweaks to the constants or through changes to the algorithm - maybe just adding a smoothing algorithm at the end.  We'll see.  The rain shadow being displaced from the mountain range I'm not so sure about.  That may or may not represent a true problem.  Perhaps the mountain range is merely not tall enough for a sharp rain shadow.

Terrain for the area above
In any case, all of this represents progress of sorts.  I need to get these issues resolved a bit further before I can start implementing the rest of the river generation algorithm.  That's because river generation is dependent upon the rainfall data to calculate water flows that ultimately lead to rivers.

That can wait until Wednesday evening.  For now, I am signing off.  Good night, world!

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