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Comment by Imnimo | Hacker News Reader

I wonder what it would take to adapt a model like this to generate non-Earthlike terrain. For example, if you were using it to make planets without atmospheres and without water cycles, or planets like Io with rampant volcanism.

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Since 1996, Ken Perlin has published a whole bunch of extremely cool Java applet demos on his web page, which he uses to teach his students at NYU and anyone who wanted to learn Java and computer graphics. One of his demos was a procedural planet generator!

I learned a lot from his papers and demo code, and based the design of The Sims character animation system on his Improv project.

https://mrl.cs.nyu.edu/~perlin/ (expired https cert)

https://web.archive.org/web/20001011065024/http://mrl.nyu.ed...

Here's a more recent blog post about a new one using WebGL, Dragon Planet:

https://blog.kenperlin.com/?p=12821

Here's another blog post about how he's been updating his classic Java applets by rewriting them in JavaScript:

https://blog.kenperlin.com/?p=27980

In practice you can use 2d generation on spheres with simple UV mapping techniques. Your pixel height becomes distance from the sphere origin.

Will it not get all bunched up near the poles though? and maybe have seam where the ends of the tiles meet?

edit: Perlin noise and similar noise functions can be sampled in 3d which sorta fixes the issues i mention , and higher dimensions but i am not sure how that would be used.

Yes, to generate a whole planet it is a much better idea to use something like a cube map.

I've thought about this before, and I think there is some way you could find to do it. For example, you could generate on the mercator projection of the world, and then un-project. But the mercator distorts horizontal length approaching the poles. I think it would be complex to implement, but you could use larger windows closer to the poles to negate this.

You're still going to run into problems with mercator because under mercator the poles project to infinity, so you'd need an infinitely large texture or you special-case the poles. Many renderers do this so it is viable!

There isn't a zero tradeoff 2D solution, it's all just variations on the "squaring the circle" problem. An octahedral projection would be a lot better as there are no singularities and no infinities, but you still have non linear distortion. Real-time rendering with such a height map would still be a challenge as an octahedral projection relies on texture sampler wrapping modes, however for any real world dataset you can't make a hardware texture big enough (even virtual) to sample from. You'd have to do software texture sampling.

Yes, you can use a 3d Perlin noise field and sample it on the surface of the sphere, to get seamless texture without any anomalies at the poles or projection distortion. That applies to any 3d shape, not just spheres -- it's like carving a solid block of marble. And use 4d Perlin noise to animate it!

It's easy to add any number of dimensions to Perlin noise to control any other parameters (like generating rocks or plants, or modulating biomes and properties like moisture across the surface of the planet, etc).

Each dimension has its own scale, rotation, and intensity (a transform into texture space), and for any dimension you typically combine multiple harmonics and amplitudes of Perlin noise to generate textures with different scales of detail.

The art is picking and tuning those scales and intensities -- you'd want grass density to vary faster than moisture, but larger moist regions to have more grass, dry regions are grassless, etc.

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