Devil's postpile?

Geology and Terrain
1

I’m not even sure where to start, but I’d REALLY like to include a feature like this in a terrain:

http://members.cox.net/mcamann2/Postpile1.jpg

http://members.cox.net/mcamann2/Postpile2.jpg

Both images are copyright Abe Kleinfeld, linked without permission for illustrative purposes only. :wink:

on edit: hosted the images myself.

Any advice about where to begin would be much appreciated!

xoxo
Mike C.

2

hoo-wa! :slight_smile: very nice things… hmmm… Well, a few ideas pop to mind:

  • to make a discreet ramp (aka steps): can be done with several height selectors, or even better a terrace device.
  • to make granular pieces of terrain (square): can be done by zooming out to loose information, and zooming in again to get one pixel as a square area. (there are macros for “zooming”) - The trouble with this thing is it is only good for square shapes… :frowning:
  • a better alternative to doing the previous is to use an expander device, to inflate a probability device…
  • the hexagonal shape reminded me of some celular noise thing… so very related to Voronoi usage… possibly the best way to get the shape out of a voronoi is to feed it to an expander device (in Tigthen or Min) and then invert the result.
  • I don’t know if a clamp device could also help a lot in getting a heigher slope from the voronoi shapes…

PS - this thread could be moved to the new geology discussion forum; makes sense there :slight_smile:

3

Yes, i guess voronoi would be the best thing… in one of the “cells” styles.

4

I’ve been playing with the voronoi to try to get that… But it’s not easy. The “clossest” results I get are using F2 and F3-f1… but each column is very far appart. They also tend to be the same height wich spoils the effect… I don’t really think there is a good way to do this in a macro…

Unless I somehow displace a dradient to try and sample the column’s height at more random places to get the the different-height cristal shapes… This is though!

This was the best I could come up so far… Very uggly, I know :frowning: (crystals.tmd)

5

Yes… the devil’s pile is a type of columnar basalt. There’s some good examples in washington, where I live, near the columbia river as well.

This is a difficult one, mostly because the distinguishing characteristics are the vertical columns; something that is a bit hard to capture in a heightfield.

The other problem is that this is really a pretty fine-scale thing; each column isn’t very wide, which will require a high-detail terrain to capture.

You can get hexagon-ish cellular shapes from the Voronoi generator, but from there to exposing them on a hillside is a different story. What’s really needed is some sort of “shape tesselator” device that would take an input heightfield and a shape, and recompose the input heightfield out of a tesselated field of the given shape.

6
the hexagonal shape reminded me of some celular noise thing..

Hey Fil, you’ve already done the hexagon shape. vv Lego

http://img.villagephotos.com/p/2004-10/854697/fIlego.jpg

7

I’ve made a macro in order to (try to) produce the hexagonal shapes…

It requires Standard version, because it uses Blur devices and two Voronoi types.
It’s not complete yet… It’s late (4 am), and I may continue it tomorrow. Until then, don’t hesitate to improve it or to give me suggestions…

http://terrafgen.free.fr/Downloads/Macros/WM1/Postpiles.dev

8

I’ll let you know how it checks out. :slight_smile:

9
Hey Fil, you've already done the hexagon shape. vv Lego
Err.. yeah, but that is cheating :), as it is plug-in and not a macro :P

But thinking on Stephen’s hint… I think it would require some sort of “computer vision” techniques, to flood-fill some area, and tesselate it (find contours)…
This actually gave me another idea to follow:
Another alternative, for the case of the voronoi, is to spot the places where the walls of the voronoi meet (flat regions, or at least the locally tallest pixels) This might be doable in a Macro, by applying a expander device after the voronoi, and selecting all non-horizontal content (with the exception of the lower areas)
This would mean voronoi → expander → (select slope masked by select height)… sounds complicated, I’ll test it later today…

10

Ok, after killing my head arround for some time, I think it is best to stick with the cells from voronoi, and not use the normal F1, F3-F1 functions as I was using…

So for that it came to mind that I needed one of the following things:
:arrow: a spetial Height Selector that would select height near the height region of a given heightfield (so if H1 goes from 0.2 to 0.3, I would select heights between .2 to .3)
:arrow: a Inverse-Clamp device that would return two scalers with the lowest and highest heigh values on a terrain. (the Equalizer doesn’t quite do what I want)
:arrow: an different expander device that would expand according to height variations (if height varies very drasticly it would expand less in that area: it’s not the same thing as the current use of the mask input)
:arrow: an optional input port on the voronoi to make the cells the height of another heightfield.

11

I updated the macro! It uses less devices, and should build far more quickly. I tried to reproduce the effect of the second pic only, not the first one.

http://terrafgen.free.fr/Downloads/Macros/WM1/Postpiles.dev

12

Nice! That makes a nice approach to the postpiles on the ground, yes!
In fact I thought the piles had to have a flat top, and now I see they really don’t…