How to create stones like karren?

[kalwalt]

Maybe you are wondering what is a karren, this is a typical geological formation of the carsism. I live in Trieste (IT) and it is very famous for this. for a description in English go in the speleo web page http://www.speleogenesis.info/directory/glossary/?term=Rinnenkarren, in particulary the page point to "Rinnenkarren" in which i would more interested to realize. See also the picture attached, taken from this site http://www.oberstdorf.de/alpininfo/allgaeuer-alpen/geologie/helvetikum.html ; i think i can figure out how to realize the stones but not how to applly the typical erosion from the water streams ( see in the picture in the foreground, those channels are 1-3 centtimeters large), What should in your opinion the best approach to realize this?

Thank you,

Walter

[mhaze]

StretchedPF?

[archonforest]

 ???What is PF means

[Hannes]

Power fractal

[archonforest]

Thank you Hannes

[kalwalt]

yes maybe a stretched PF could work, but with a PF, the magnifying detail continues indefinitely? how can i stop the detail?

[Tangled-Universe]

yes maybe a stretched PF could work, but with a PF, the magnifying detail continues indefinitely? how can i stop the detail?

In the powerfractal the "smallest scale" is the size of the smallest detail the fractal generates.
As you may know, scales in TG are metric.

So increasing smallest scale is what you may be looking for.
Another way to control the detail of the fractal is the "Displacement roughness" setting in the displacement tab of the power fractal.

Basically this setting controls the drop-off for how fast the amplitude of octaves/scales decrease.
For example, at a setting of default 1 the drop-off is half the amplitude for each next octave.
A setting of 0.5 will make the drop-off stronger, thus removing smallest scale features of the fractal.
A setting of >1 will make the drop-off weaker and at much greater settings than 1 you are even capable of reversing the "profile" where small scale octaves have larger amplitudes than bigger scale octaves.

[kalwalt]

Thank you Tangled-Universe for the quick and very comprehensive answer! Your reply has dissolved all my doubts, I will work on this now.

[mhaze]

Sorry I didn't answer more fully - in addition to TU's suggestion you can use colour offset in the colour tab - just set it to a minus value and play.  I find it useful to click on the blue square at the top right of the power fractal pop up to get a visual of what's happening.

[Tangled-Universe]

Sorry I didn't answer more fully - in addition to TU's suggestion you can use colour offset in the colour tab - just set it to a minus value and play.  I find it useful to click on the blue square at the top right of the power fractal pop up to get a visual of what's happening.

The colour offset and other colour settings won't affect the displacement if you have displacement enabled within that PF node.

If you want to control the displacement with the colour settings then you must disable displacement in the PF, connect the PF to a displacement shader's "function input" port on the right and then the colour output of the PF will be converted to displacement.
Make sure that the displacement shader replaces the PF in the node network chain, meaning that the PF won't have any input connected to it anymore. Important!

Then the offset, contrast and roughness settings will control the displacement, but also the chosen colours themselves.

[kalwalt]

Thank you for the clarifications @mhaze and @Tangled-Universe, actually i'm creating the heightmap with WorldMachine, when it will be ready , i will start to experiment with PF nodes!

[mhaze]

Well TU, I didn't know that!  That actually clears up a couple of problems I've had.

[Dune]

I'd say use a stretched ridged perlin PF of very low octave and size and restrict that by max slope. I see some areas of the stones are worn out on the top; you can do that by adding a negatively displaced perlin PF (also not too many octaves), also restricted by max slope.
The squarish stones are harder to get, you might try a combination of X and Z stretched fractals to displace them vertically. Room for experiment...

[kalwalt]

I'd say use a stretched ridged perlin PF of very low octave and size and restrict that by max slope. I see some areas of the stones are worn out on the top; you can do that by adding a negatively displaced perlin PF (also not too many octaves), also restricted by max slope.
The squarish stones are harder to get, you might try a combination of X and Z stretched fractals to displace them vertically. Room for experiment...

yes, Ulco this is a work in progress! and you gave me a good input, i will soon show something of the experimentation....

[kalwalt]

Finally some experiments: first picture karren-without-shaders show a particular of the heightmap created with Worldmachine wiyhout shaders applied.
[attach=1]
this instead is with shaders applied, more or less as suggested by Ulco, but for the crack i used this clip from @dandelO http://forums.planetside.co.uk/index.php?topic=8849.0
[attach=2]
this is a screenshots of my nodes shaders.
[attach=3]