WIP - Batai

[Master TMO]

I'll try lowering the sea level there and see what it does. But the elevation of the area ranges from 2k feet in the NW to 1000 in the SE. It's not really that close to sea level. And it also didn't affect the Great Desert, which is over a mile above sea level (but rainfall might have affected it - I don't know if Incise Flow uses potential rainfall or actual, I assume actual).

[waldronate]

What's your editing resolution? If it's fairly low then the slope on the canyons might be shallow enough that you can't really see much.

[Master TMO]

4096 - not very low. I'm wondering if maybe this beta version I'm working with is only grooving down original terrain, and not new? I'll run some experiments and see if it seems like it or not. Might just be a glitch in the new model. I'll let you know what I find. Thanks for the help so far!

[waldronate]

Things should be visible at that detail. The process FT uses is: evaluate the surface, fill basins, find flow amounts, subtract flow amounts (with specified exponent and results clipped to 0) from the offset channel. The next screen refresh will recalculate the world with the changes.

It's possible that you're using a large blur and/or a large Amount, which can result in large areas of the higher flow (effectively farther along the rivers) being forced to 0 and so having no visible effect. What settings are you using? Try an amount of 1, flow exponent of 0.3, effect blend of 1 and blur of 0. If those settings don't result in visible channels in areas not at sea level then nothing will.

Wilbur is a good tool for learning the incise flow settings. It has faster setup and is a little bit easier to fiddle with.

[Master TMO]

Flow settings the first time were 1, 0.667, 1, 1. I've also used 1, 0.667, 1, 0. (0 blur)

[Master TMO]

Hrm. Maybe I'm just expecting it to do something it doesn't do. Attached is a screen cap from a section of a different map, in pristine untouched condition. I found a basin area to test pre-basin fill incise flow vs post. But on the pre-basin fill, it still didn't carve any canyons or riverbeds on the flat areas, only on the slopes. Is that the expected result?

[waldronate]

Ah, now I see the problem. The basin fill operation is very important because it connects all of the land pixels to the sea pixels. The underlying fractal function is full of pits at all levels. When the flow calculation reaches a pit it stops. The incise flow operation is not a true fluvial simulation in that it does not accumulate water and move sediment. It only incises the existing flow into the underlying terrain.

A true fluvial simulation involves rainfall (adding water at each pixel), flow (moving water and sediment at each pixel), and evaporation (removing water at each pixel). This sort of operation is extremely compute intensive and suffers from a serious scale problem. Water flow simulations start to lose their versimilitude when pixels get much larger than a few meters. A basic fluvial simulation run at a worldwide level just looks wrong. The features it generates are inappropriate for ten kilometer-sized pixels.

Consider the precipiton computation in Wilbur. It is not a complete fluvial simulation, but people seem to like the way it looks. The way it works is that the system picks a random pixel and moves terrain height from that pixel to its lowest neighbor. This process repeats until the "flow" gets to a pit. A new random pixel is then selected and the operation starts again. It's totally unrealistic but works because your eye wants it to work. It's much the same way that basic fBm noise can look like a terrain at first glance.

If I ever find a good simulation that does plausible erosion on low-resolution maps then I'll probably include it in FT. I haven't found one, though. At this point FT can't generate endorheic basins like the American west or the Taklimakan basin that hosts the Gobi desert due to a lack of correct water flow computations in the terrain model as well as lack of air flow computations in the climate model.

[Master TMO]

Ok, I understand. I have been asking it to do something it's not intended for. No worries! Knowing that, I'll mess about, see what I can do, including Wilbur. Sorry to spend so much forum bandwidth on the subject. Back to the map! *plays dramatic action movie music*

[Master TMO]

I think I'm about ready to finish this one. I just need to clean it up and see how the client wants to see it. I'll try to do a GoogleEarth shot of it over the weekend and post it. There's nothing significantly changed from the Pretty version posted above.