Hills and Rivers in Wilbur with Fractal Noise

[Coggleton]

Hello,

I've been working on a map in GIMP for a while, and I've already made the elevation ranges in GIMP and was wanting to use Wilbur to create my hills/rivers. I've got the elevation map into Wilbur, and have something like what you can see in the picture below.

wilbur sample.PNG
Note how the different elevation ranges are different monochrome regions. Image is 22500 wide x 11250 height.

I'd like to get a range of noise and hills/ridges for each elevation range (Green, Yellow, Orange, etc.), but when I run fractal noise with the relevant range selected I get a monochrome teal-green:
wilbur teal.PNG
Instead of being filled with interesting ridges, I have pea soup.
wilbur fractal noise setting.PNG
These are my fractal noise settings

Running the same settings without the area selected actually works:
wilbur noise.PNG
Fractal Noise covers the whole map

My Questions are:
a) Why can't I get Fractal Noise to generate inside the selected area? I've been able to do it in smaller maps, and it works when there's no selection; any ideas on what's going on?
b) Suppose I do get Fractal Noise generated; is there anyway I can "squish" it down so my mountains become hills?
c) Is there a better way of creating "hilliness/rivers" starting from the first picture? I know there's tutorials for generating these maps with clouds, however I've already made my elevation map, and at my map size the clouds aren't really feasible?

[Greason Wolfe]

Try changing the Operation to Add or Multiply. You currently have it set for Replace which, well, replaces the height data that is already there. Alternatively, you could wait for Waldronate to see this question and offer some spiffy answer that will be way better than my suggestion.

[waldronate]

What are the altitude ranges for each range? You're telling Wilbur to fill the selected area with fractal noise from 0 to 1 (Amplitude), which will show as constant green If the maximum value in your map is much above 100. As Greason Wolfe suggests, use multiply as the operation if you want to keep the maximum altitude roughly what's shown in your map. If your ocean is 0, using multiply can let you apply the fractal noise to the entire surface at once without having to select each altitude individually.

I don't recommend using a surface that large, especially for initial roughing in of the terrain. Fill Basins is likely to fail with a crash and performance using Incise Flow is likely to be "maybe it will finish". Starting with a much smaller surface and scaling up to your final size is much more likely to be effective.

The shown portion is a crop of a much larger piece, correct?

[Coggleton]

What are the altitude ranges for each range?

After trying to sort it out via selection->height ranges in Wilbur, I have the following ranges (each color is a single value within that range, but I don't know the exact value of that color):
1-100
101-110
111-120
121-200
201-220
221-250
251-300

I don't recommend using a surface that large, especially for initial roughing in of the terrain. Fill Basins is likely to fail with a crash and performance using Incise Flow is likely to be "maybe it will finish". Starting with a much smaller surface and scaling up to your final size is much more likely to be effective.

Is it possible to scale the image in Wilbur? I tried the Scale function, but it didn't do what I think it did. While I'm on the subject, what do Scale and Span (Under Filter->Mathematical) do?

The shown portion is a crop of a much larger piece, correct?

Correct.

[waldronate]

One quick way to see your height ranges in Wilbur is to use Window>>Histogram. It will show you how many of each altitude are present in the image.

With the ranges that you're showing and using replace as the operation, it was definitely just losing detail as it set the altitude to zero.

Adjusting the number of pixels in an image in Wilbur can be done with Surface>>Resample>>Simple. Why Resample instead of scale? It's a long and ugly story having to do with Wilbur's history, but resampling is changing the number of pixels in the image, while the Scale filter adjusts the magnitude of the altitudes. The Span filter is for those too lazy to do math: it finds the existing minimum and maximum values of the surface, then applies a linear scale to remap that range to the one specified.

[Coggleton]

Going off the rough estimates between Bin Low and Bin High, it looks like my heights are the following:

68
103
114
157
209
236
254

So just using "Multiply" should rectify the issue without causing, say, a peak with height 220 among a plain of 60-70, correct?

And on the subject, would you happen to know what the rest of the settings in Fractal Noise mean?

[waldronate]

Correct. Multiply with an amplitude of 1 will yield values between roughly 0 and the existing altitude.
For the most part, you shouldn't need to mess with the things in the left-hand column (H, Lacunarity, and so on). Those are the parameters for the ancient Musgrave fractals as described in Textures and Modeling: A Procedural Approach. Some internet searching should get you appropriate information if you really want to play with them (Musgrave and Lacunarity will get you some good hits).
The right-hand column is probably more useful. Amplitude is the scaling for each point on the fractal. Displacement is the offset for each point on the fractal. XY Scale give the horizontal and vertical feature size for the fractal. XY Origin sets where on the plane the fractal is located (moving this will give the appearance of different fractals). Seed is the random number generator for making the fractal. Each one gives a different fractal if all other parameters are held the same.