Merging fractal detail

[bigben]

Hi All

Another thing that I'm revisiting is trying to find a way to add more realistic detail to TER files.  Fractal detail is pretty good but there are some aspects that still bug me, in particular the handling of steep surfaces.  That said, there are any aspects of fractal detail on TERs that I like more than just adding a powerfractal displacement. 

Clip files developed by others on functional terrains don't necessarily translate all that well to  a TER with fractal detail either... once again due to the difference between "fractal detail" and a "fractal terrain". Finding a combination of fractal detail and additional displacements has proven quite difficult for me, partly because it's a little out of my expertise, and partly because I'm *very* picky about my own work.

Having a play at the moment with merging duplicate heightfield nodes with different fractal detail settings.

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Some intial quick renders looked more promising than previous attempts, but I'll need to do some higher detail tests to be sure. It's a fairly simple node structure which is another thing I like about it. Fingers crossed    

If it works for a 10m terrain, the next test will be a lower resolution terrain (ie TER from 90m SRTM3). I've gotten a bit closer with fractal detail settings for these terrains, but a single displacementnearly always ends up looking computer generated in some parts, or doesn't provide enough extra detail.

[bigben]

Test image 1.
Single heightfield shader, no extra displacement.

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Most of the displacement on the steeper surfaces looks too much like an erosion filter with a very uniform setting (but much better than no detail at all, or a uniform fractal displacement). 

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Additional variation by merging two different versions of the same heightfield with different fractal detail settings.

[rcallicotte]

I never knew this wasn't possible with heightfields and steep surfaces, until now.  This is very useful...to know what can be done and now to understand how to do it.  Thanks.

[Alfamike]

Hello,

I have used this in the past trying to generate thick snow.

Take two heightfields that only differ in the amount of surface detail, one smooth (snow) and one rough (the original landscape).

Offset the snow one vertically a little. Then merge by highest elevation.

It works to some extend, but you get valleys that are filled up smoothly, but also bits of the original landscape that are without snow. You could apply thin snow to those, but I stopped it there, as I was not happy with the results.

AM.

[bigben]

It's not quite like making a snow "terrain" as the end result is a single terrain.  It's more like your stacked power fractals, mixing fractal detail of differing scales to produce a better end result.  Attached a screengrab of this method applied to one of my basic tiled terrain sets.

The high resolution terrain is connected to 2 heightfield shaders with different fractal detail settings. These two are then mixed together using a merge shader.  The masked padding terrain is then added to the result via another merge shader with a merge mode of "Add". To simplify things in future I think I'll put the high resolution terrains at the top and then simply feed the merged result into the input of the padding terrains.  There's no point getting fancy with the padding terrains as they're not intended for a close up camera view.

[bigben]

One thing I found with this is that it requires a constant scalar connected to the mix controller (with a vlaue of 0.5) to work as expected. Without it you only get the first input.

I'm working my way through Tangled Universe's canyon tutorial, adapting it to my TERs. The scales are very different but I'm starting to make some promising progress with better displacements.   About half way through. The main problem I have at the moment is some spikes in one of the first 2 PF displacements, but I'm fairly happy with the progress. Converted to greyscale to concentrate on the displacement.

[rcallicotte]

This is fantastic!!  Realistic vertical bumps.  Groovy.

[bigben]

Thanks.  Here's the reference image.  Just the raw terrain, no fractal detail

[rcallicotte]

Thanks Ben.

I need more time.