How to make these Rocks?

[fxsculpt]

Hi, Im new here and could use a few tips from the experts here. I would like to get results even close to what are shown in this image here.

http://forums.planetside.co.uk/index.php?action=dlattach;topic=4413.0;attach=11748;image

I have been trying for few weeks (pouring over the forums and NWDAsite) and have created some interesting images but my problem seems that proper Power Fractal scale settings seem to be the key to the realism of the result. Are there any tips on the "scale of noise" for creating rocky cliff faces? Any chart that breaks down what noise scales should be used to get rocky looking surfaces like the image above?

For example I have a 1000m tall cliff what Feature, Lead & Small scale settings should be used for my Redirect shader noise. And what Strata and Outcrop shader Depth & Spacing should be used? For me its been a fun guessing game of sorts. 

How can I get this?
http://www.walesdirectory.co.uk/images3/Great_Orme_Cliff_Face.jpg
http://www.a2bwales.com/images/daysout/southerndown7.jpg
http://www.goulburnvalleyreptilesupplies.com.au/images/234%20Cliff%20Face.jpg

Thanks I really appreciate any tips on this.

[TheBlackHole]

Just play with the scales until you find what you like.

[FrankB]

not a very helpful answer, TBH, I'm afraid.....

so, fxsculpt, you need to think about what the average size of your main rock feature is. For example if you have a 300m x 300m steep rock wall, *maybe* a feature size of 50 will look good for larger features (the feature scale).  The smallest size will determine how much detail the power fractal will produce. Actually the octaves will determine the detail, but of you lower the smallest size, the octaves with increase automatically.
As a starter, in this example, you might want to choose a largest scale of 300, but you can play with increasing or decreasing this.

To get overhanging strata layers, you need to "twist and shear" your rock wall so that it overhangs, and afterwards apply a strata and outcrops shader, and a powerfractal with lateral displacment for additional bumps.

Hope this can get you started.

Frank

[fxsculpt]

Thanks for the suggestions. They do seem to make sense.

"As a starter, in this example, you might want to choose a largest scale of 300, but you can play with increasing or decreasing this."

By largest scale here do you mean the "Lead-In Scale"? So for example If I have a 500m - 500m wall, I may think a 75m Feature Scale may look good but I should set Lead In Scale to the largest size of my wall?

So in this case Lead In Scale I should start with 500m?

If not what is the best way for me to think of lead in scale in terms of the visual end result?

Thanks for the help. I will post some images once I get something looking ok.

[FrankB]

yes I meant lead-in scale. ... If I were to describe it in my own words I would say lead-in scale is the maximum size of clumped-together feature (sizes).
You can try this out yourself:
If your lead-in equals the feature size, then the features will be relatively evenly distributed, with a space between them that equals the feature size.
With your lead-in scale being 10 times larger, you get "areas" 10 times the feature scale, which is full of your main features. But you also get spaces between these areas that are as large as the lead-in scale.

I think the best way to understand this is to just take a power fractal, double click it and watch the shader preview in the upper left, how the distribution changes as you adjust the lead-in scale relativ to the feature scale.

Sorry, I can#t think of a better way to decribe this. I realize it sounds a little bit difficult.

[Tangled-Universe]

Another "simple" way of determining scales and which might help is to open the image in a editor and draw in the estimations of the scales.

For example:

the absolute height of the entire structure
the sizes of the major features
the sizes of the intermediate features
etc.

These measures may not represent real-world scale but that's not important since you can make it look like any scale you like.
This way you only need 2 powerfractals most of the times, which you can handle pretty well.

I will try to dive in some of your examples and see if I can work something out.

Cheers,
Martin

[FrankB]

I use the built-in measure tool to determine actual scales, Martin. Very handy.

[Tangled-Universe]

I use the built-in measure tool to determine actual scales, Martin. Very handy.

That's what I also do, but don't forget that this is INside TG already.

I was explaining how to get an idea of which scales to use by analyzing it a bit in advance in an editor or just inside your head and after that firing up TG2 and start doing it.
Next handy thing for assistance is indeed the measure tool.

[fxsculpt]

Great tips guys. Thank you. I try to use the measure tool as well. Its useful. I wish that tool worked on top of the rendered image at times.

After I get the scale of the softer fractal bumps the way I like, how are you guys creating those sharper rock like forms (various planes that make up the basic rock structure) for the stones (like the images)? Is this just a matter of using extreme displacement values?

[FrankB]

can you point to a particular example? There might be multiple ways, and I am not sure I understand your question.

Cheers,
Frank

[fxsculpt]

Something like this image..

http://coastal.er.usgs.gov/navassa/photos/lb/sail/CliffFace2.jpg

Are you able to view that?

There are large structures but also smaller ones but all have nice well defined surface planes and then there are these large vertical cracks running through. When you have for example an art director asking you to create this what would you do here?

[FrankB]

well this is much more complicated.
If time to production plays a role I would probably use a displacement mask,  derived from a photo, and project this onto the plain wall.

If I need a world to explore, and not just one narrow scene, I would have to tackle the problem procedurally, at least in part.
For the cracks you need to employ a voroni based function. The voronoi can also give you these rectangular stones.
Having the wall enhanced this way, I would add a series of fake stones to the rock wall, to add more detail.

I've made the wall in this image once, using both voronoi and fake stones: http://www.nwdanet.com/buy-packs/8-object-packs/11-bushes/41-lilac-syringa-pack.html

Regards,
Frank

[fxsculpt]

"I would add a series of fake stones to the rock wall, to add more detail."

Wow great tip! I can see some results already from your suggestions. I just need to play with the scales. I love the Fake rock shader (nice surface structure in there ) in TG2 but I did not think of using the fake stones on the side of a wall?! Great.

BTW I have purchased several of your packs from the site. Very help indeed.

Thanks again for the tips everyone.

[FrankB]

Glad to have helped you.

And yeah, although one could think otherwise: fake stones that grow on a steep wall stick there, and won't fall off

Cheers,
Frank

[inkydigit]

exactly what I was thinking Frank...voronoi(possibly with fractal input?) and lots of fakestones on the cliff wall, this way you can get some pretty complex knobbly and flakey structures!