View Full Version : Making a decent volocano...

03-16-2014, 03:40 PM
Hello all;

After diligently pouring over the Tutorials & How To's, and after hours of experimentation, I STILL cannot build a decent volcano with GIMP. I'm trying to get a nice, conical, textured island-type (think Oahu or Hawaiʻi - the island, not the whole state :lol:) - but with no luck as of yet. The only tut I found resembles pools of lava flowing down into other pools of lava; geologically interesting, but not quite what I'm after. I have the image in my head (have been up close and personnel with several that are typical for the type I'm after), but can't translate that image to the software.

Any direction would be greatly appreciated.


03-16-2014, 06:22 PM
It's not GIMP and it probably isn't quite what you were looking for, but I like it...

Greason Wolfe
03-16-2014, 08:41 PM
Oooh! I like it.

03-17-2014, 12:11 AM
It's not GIMP and it probably isn't quite what you were looking for, but I like it...

What or how did you start this? With an ellipse? I can't quite figure it out...

03-17-2014, 01:42 AM
The gradient tool in Wilbur draws slopes. One setting for Type is "Radial", which draws a cone with the value at the outer edge equal to the value "Low" in the gradient toolbar and the center equal to the value "High" in the gradient toolbar when you click and drag. Using the same tool but with the center value equal to a lower altitude and the operation to "Min" (minimum), the gradient will drop out the center of the cone. Most of the rest of the operations (noise, incise flow, precipiton erosion, and exponentiation) are the standard prettying operations I tend to use in Wilbur. The only difference here is the use of morphological erode to get rid of the little spikes of noise that the operations leave.

Wilbur really needs a median filter, but I haven't gotten around to that. The Morphological Dilate and Erode filters are similar, being a local max and min operation rather than a local median operation. A better algorithm would have a patterning element rather than just using a 3x3 square neighborhood, but you get what you get.

Maybe this GIF will help. You get two seconds per frame, but it does loop.

03-17-2014, 05:41 AM
well, from one Desert Rat to another, that will do just nicely, tyvm.

03-17-2014, 11:26 AM
One thing to note is that I didn't quite use the same values in the GIF that I did in the first posting. One of the tricky/annoying/useful aspects of the algorithms in Wilbur is that they're sensitive to scale because they work in pixels, not abstract units. The precipiton erosion feature, for example, always generates channels that are some number of pixels wide; the morphological operations are always operate on an area 3 pixels wide; the incise flow operation deals with flow across image samples (pixels); and the blurs are defined in something that works out to be pixels. How large the effects of each of these activities appear is relative to the overall image is a function of the size of the image. The information in the GIF uses a 256x256 image, while the other one is a 512x512 image. Note the subtle differences. As a benefit, the smaller image processes much faster than the larger one (some of those algorithms are O(n*n*n), meaning that an image half the size may take 1/8 the time).

A loose version of the classic definition of a fractal deals with the notion of a motif repeated across scales. An entertaining use of Wilbur is to do the bulk processing of a surface at relatively small size (256x256 is a good starting size), scale the surface up by a factor of 2 (or thereabouts) and then apply processing for higher details. A common processing operation in Wilbur involves basins fills and incise flow. Both of these operations are fairly slow, but the incise flow is especially so. By roughing in the shapes at lower resolution, it's fairly quick to get something done. The attached crop of a 4kx4k image done via scale-and-add shows what 10 minutes of processing will do (I forgot to punch out the crater, so it's just a mountain). Trying to get this same level of effect by starting at 4kx4k usually takes me about an hour.