Tectonic plate fakery

[aidenprice]

After a very long time lurking I'm finally in my element and need to post.

I don't suppose you could indicate on your examples which plate boundaries are convergent and which are divergent could you? Just some simple arrows pointing in towards or away from each boundary would do.

It would be very useful in critiquing the results. Not that I'm trying to sound disparaging, I think this will be utterly brilliant.

Aiden

[isomage]

I don't suppose you could indicate on your examples which plate boundaries are convergent and which are divergent could you?

Sure. I've also changed how the boundaries are made: the previous version had each plate either expanding or contracting on all edges (which wasn't very realistic but seemed easier at first glance), but now the individual boundaries themselves are randomly determined.

Here are some new maps, still suffering from the same discontinuity problems, but now with transform boundaries in gray, divergent in blue, and convergent in red.

[Redrobes]

AidenPrice: Welcome, post an intro message Your handle rings a bell from distant memories too but I cant think why. Anyway, good to see you here.

Isomage: Good stuff. I agree that rand terrain generators suffer in the way your trying to fix and this looks like a good way to do it. Interesting. I think su-liam uses libnoise too - you might tap him if he comes on line too. Its looking good so far so keeping an eye on this.

[aidenprice]

Isomage; Looking better.

- Randomly assigning convergent/divergent/transform does lead to a few unlikely situations, like the middle plate in map 1 where there are convergent boundaries on opposite edges and divergent ones opposite each other on the other edges, though I don't know how you'd fix that without simulating all the stress and movement on each plate which is way beyond what is necessary.

- The divergent boundaries look good, the reason being that divergent boundaries create sea floor that is the same elevation on both sides (worry about mid-ocean ridges later I reckon). Unfortunately that works against your convergent boundaries which tend to be a bit more one sided, even when two continents collide, it depends on which of the two plates is subducted. Perhaps offsetting the height field only for convergent boundaries might work (he asks with no real idea what he's talking about)?

- A similar sort of offset could work well for a transform boundary (along the length of it though, rather than away from it) moving parts of continents in opposite directions.

Sorry to sound like a critic without offering any real help.

Redrobes; Intro posted, really looking forward to seeing some more of Geotersys!

Regards,

Aiden

[isomage]

- Randomly assigning convergent/divergent/transform does lead to a few unlikely situations, like the middle plate in map 1 where there are convergent boundaries on opposite edges and divergent ones opposite each other on the other edges, though I don't know how you'd fix that without simulating all the stress and movement on each plate which is way beyond what is necessary.

Yeah. In a final map the plate boundaries will be omitted, though, so you wouldn't notice that kind of thing.

Perhaps offsetting the height field only for convergent boundaries might work

That's basically what I'm doing, but where I have a convergent boundary next to a non-convergent one (as two adjoining edges of a plate), I get a discontinuity in the plate's terrain -- I haven't figured out yet how to blend the terrain smoothly between the two boundary influences.

[isomage]

I think I may be getting somewhere...

[Kestenvarn]

Looking neat!

[RobA]

Looks quite promising! Are you ready to crank up the resolution and bit depth now, and give us a real example instead of these teasers ?

-Rob A>

[haroim]

looks very good! I have been trying other software, but with only fractals it doesn't look very realistic. When will the first test version come out?

[isomage]

I think any kind of release and examples with more detail are going to have to wait a bit -- I was able to solve the discontinuities but only at the cost of a huge increase in rendering time.

The basic method is still to divide the sphere into Voronoi cells from 8 randomly distributed points, and perturb the cell boundaries with noise, and randomly assign each boundary one of the three types, but I've changed how the cells and boundaries filter the underlying fractal field.

Each cell contribues either a medium or low value (randomly selected per cell) which increases to 1 at its boundary; thus some cells will tend to preserve the height of the underlying field, and some will lower it, so that's how we get continents and oceans. This is averaged with another value based on a point's distance from a convergent plate boundary, being 1 at the boundary and dropping off exponentially with distance. That average is then multiplied against the base fractal field. Thus we're more likely to get high elevations along or near convergent boundaries, and these may be coastal where they're between a high and a low cell, in the middle of a landmass where they border two high cells.

Getting the ridges on the convergent fault lines has required an additional pass through all the points on the map, where points lying on convergent boundaries are identified and stored so that in the final pass each point's distance from its nearest fault point can be found, and that's slowed things down a lot. I might be able to speed it up if, for example, I don't count all the points on the convergent faults (perhaps finding only ones which are farther than some small distance from previously found ones), but I'll need to play with it.