Author Topic: stretched terrain  (Read 1556 times)

Offline digitalguru

  • Member
  • *
  • Posts: 449
stretched terrain
« on: March 25, 2013, 03:23:16 PM »
I've made a terrain in world machine that has a punchbowl type crater depression with very steep vertical walls. My problem is that when applying displacements to wall of the punchbowl, they get very stretched at the the point where the vertical slope is the steepest (i.e almost perpendicular to the ground plane).

I guess this might be a limitation of the .ter file I'm loading as a heightfield as it's essentially a bitmap and there's probably not enough bit depth to represent a sharp gradient?

It may be that I've dug myself into a hole trying to make this kind of terrain (pun intended) - but has anyone come across this before and have some tips to share?

Offline Tangled-Universe

  • Terrevangelist
  • *
  • Posts: 6183
    • CGScenery.com - Terragen Tutorials!
Re: stretched terrain
« Reply #1 on: March 25, 2013, 03:30:10 PM »
It is known that in TG the walls of sharp displacements are low on subidivisions and generate very stretched polygons and textures.
TG interpolates the values of your heightfield to create more "depth" as you refer to.
It could be a bit of both then if your terrain is really low on resolution, but usually TG handles this pretty well and thus I think it's rather a TG thing.

Offline digitalguru

  • Member
  • *
  • Posts: 449
Re: stretched terrain
« Reply #2 on: March 25, 2013, 03:49:14 PM »
hi Tangled,

tried the highest rez terrain I could generate, but alas no joy, and thought a compute terrain with a small patch patch size would "recompute" the normals to fix it?

but as you say might just be a limitation of using 2d data to compute a 3d terrain...
« Last Edit: March 25, 2013, 04:30:07 PM by digitalguru »

Offline Hetzen

  • Member
  • *
  • Posts: 1653
Re: stretched terrain
« Reply #3 on: March 25, 2013, 04:11:42 PM »
As I understand the effect you're after. You might want to look at the HF as an influence mask on another fractal that gives you steep sides and cuts like a billows noise. If there's enough graduation grey in the map, (you could do this in TG with simple shapes), you can then use bias or gain to form the basic shape of your crater. The advantage of doing it this way, it gives you the ability to control the steepness of the sides, therefore giving TG more 'top-down' information on the slope to draw more facets. Once you have your base shape, you could export this into world machine (use a HF generate, right click and save .ter) to erode or form further.

Offline digitalguru

  • Member
  • *
  • Posts: 449
Re: stretched terrain
« Reply #4 on: March 25, 2013, 04:25:45 PM »
thnaks both to Hetzen and Tangled Universe for your replies

Hetzen:

Sounds like an good alternative to bringing in a terrain from an external program - at this stage sculpting the terrain seemks a better bet as we're matching a re-world terrain and the layout feature in WM offers a bit more control for our needs

Think I foud the issue though, thinking about the low patch size in the compute normal helped, back tracked to the heightfield shader and turned off the fractal detail and the streching issue is gone.

Guess the fractal detail in the heightfield shader has no benefit of a compute terrain node before it and so will stretch on steep sided terrains -

Wonder if this is possible to compute before or even inside the heightfield shader (in a future version?) to get round this?

or have the fractal detail as a separate node - I really like the displacement it offers, but never found a good way to replicate it with other fractal shaders

Offline Hetzen

  • Member
  • *
  • Posts: 1653
Re: stretched terrain
« Reply #5 on: March 25, 2013, 04:50:49 PM »
Yeah, adding fractal detail does kind of pixelise the HF.

Offline Dune

  • Member
  • *
  • Posts: 15131
    • www.ulco-art.nl
Re: stretched terrain
« Reply #6 on: March 25, 2013, 05:01:21 PM »
Ticking 'smooth terrain' in the compute node may help as well, although it might indeed smooth the terrain too much, which you can overcome by adding height to it.

Offline digitalguru

  • Member
  • *
  • Posts: 449
Re: stretched terrain
« Reply #7 on: March 25, 2013, 05:16:41 PM »
thanks Dune, make a big difference - getting the patch size right is also critical to much either side of my patch size of 1 and the displacement falls apart

using voronoi to make some clumpy rock displacements - starting to come together