Strata

[efflux]

Hi Volker.

Using this to blend is very useful. I did that on my recent planet. It gives a very subtle stratification of textures to provide a natural change at altitude but you don't need anything fancy just a simple smooth blend which these nodes do nicely.

[efflux]

You may notice that the strata distorts more at higher altitude. For artistic results, this is OK. It's due to certain data flows positioning and interactions that are not so easy to explain. You have to kind of mentally backwards engineer things in TG2 to work it out.

Some things I still don't have a clear picture of. For example - get position, get position in geometry, get position in texture. For any kind of mental picture of geometry these names are completely useless. What geometry? What is texture? In Mojoworld this is all completely self explanatory. It takes about half an hour to play with and understand. Also - compute terrain and compute normal? These things all effect the positioning of things yet no clear explanations.

TG2 is a great app but if I had to give the documentation marks out of 10, I would give it 0 but this is not necessarily the fault of whoever writes the documentation. Maybe Oshyan does all that. I don't know. The trouble is you would have to have total technical understanding of what every node does and then understand how the possible geometry could be used for artistic effect. At present, nobody could actually achieve this task. A start would be clearer explanations of TG2's data flows and nodes. I can tell you now that if I hadn't used Mojoworld, I would have probably have ditched TG2 by now.

[efflux]

Well maybe 0 out of 10 is a bit harsh because there is basic instructions on how to get started but I'm only comparing to documentation of other apps.

[efflux]

For a start, there should be clear documentation on what you are actually doing when you use fractals and noise functions for colour values, displacements etc. This should be accompanied by diagrams of where and how the values are take because many people who try TG2 will not understand what is even happening here.

[mogn]

I can explain "get position in geometry" and how you derive displacement from it. The output from the "pos" node is a single [x, 0, z] value
but repeated for each point (or micro triangle) seen by the camera. Tre node tree below is called repeatly for each of these values.
In principle you first make some vector operation and then you make a transformation to a scalar (e.g a noise function, or a length function).
After this you make some tranformations and feed the resulting scalar into the second input of a displacement node.
What is important to note is that none of these oprerations changes the original point obtained from the original "get pos" point, and that
the length operationn always from the [0, 0, 0] of the current coordinate system.
In other words the process is:
   1)  select one or several points (fixpoints) in the X,Z space
   2) among these points select the fixpoint which is nearest the point you have from the get operation.
   3) Map that fixpoint onto [0, 0, 0]
   4) Convert to scalar
Conceptually the mappings that you do to the selected fixpoint, is reverse so the length you measure is mapped back (measured relative) to the
fixpoint.

   By mapping I means a transformation of the the coordinate system:

    1) Scaling. (multiply a vector by a constant)
    2) Moving the origin (subtract two vectors)
    3) Rotating the vector about y.

Have fun

[efflux]

In other words, the get position in geometry is of no real consequence if you are working with manipulating entire noise functions or fractals.

[domdib]

@mogn - I'm sure that your explanation is technically correct, but what I think efflux is looking for, and what I'm sure I and the less mathematically inclined users would like, is a simple, clear illustration. Basically, actual images of what each node can be used to do would seem the best way - accompanied by a technical description such as the one you just gave.

[efflux]

I think the get position in geometry is useful if you were building a precise geometric shape rather than working with noise or fractals.

[aymenk2003]

Okay,

my first thoughts about that strata-thingy.

In my point of view, strata is not only some sort of distorted layered displacements.
Following points should be taken into account:
1. Strata are layers of mud/stone of different heights, colours and/or hardness.
2. Unless being in an area without any earthquakes, we find tilted and/or curved strata. Enclosed stones distort the strata, too.
3. Strata can only been seen, where the topmost layer of soil is gone, so first of all we'll need an area of negative displacement.

The easiest way to achieve this would be, to use 2 or more merged Strata and Outcrops shaders (each with different tilts).
It might be funny, to use your height-driven perlin to blend those shaders.

Another approach I would go for, are perlins stretched along x- and z-axis. To give them some more interesting directions you could add some perlin driven sines to the y-position of the 'Get Position (in texture)'-Node.

I'll go for the last one ...

Volker

by the way Volker here's a real strata taken when I was back from my holiday...

[aymenk2003]

...

[aymenk2003]

...

[Volker Harun]

@Aymenk: This looks very much like the Sierra Nevada in Spain. I am no geologist, though. The vertical cracks could be due to weathered erosion.
Anyhow very interesting and inspiring photographies.

At the moment I got stuck into some functions again ... Somehow I get always drawn to do some fancy stuff.

In the Mesa's Thread of Tangled Universe is some good start for strata, I think.
Then we have efflux's Thread about Bias/Gain-Blending terrains (shaders).
Looking at the function shaders the modulo-node could be used for one set of shaders, which add height to the strata.
Another set of shaders could be based on efflux's work at the beginning of this thread.

A closer look at the photographies ... the strata is building terraces, so obviously any set of shaders for a strata should shift the existing terrain without adding much detail.

,-) Volker

[efflux]

You can hook a colour gradient into the strata. I'll post a file as soon as I get time. One has my hacked colour gradient and there is another colour gradient by mogn which I haven't tested much. I've seen two by Mogn. You want the fancy one.

[CCC]

A lot of angled strata tends to form from faults from ancient and more recent tectonic movement. You can have hundreds of faults in a hundred square mile area alone. The movement creates pressure in the rock layers that bend, twist and shift the layers about and that is where you see the warping and odd angles.

Here is a uplift strata i took a photo of while out in the lower mohave desert (In a moving car). This is very close to San Andreas.

[mogn]

Speaking of color gradients i sampled many true color earth tones and made .aco files from them that can be read in Photoshop and i hope GIMP. So if anyone want's true colors to use for that needed realism here are the color swatch files i made.

Thanks for the color swatches. At the moment I am working on a 15 color Bezier gradient using the first 15 colors from the "South West" swatch.