Clouds

Making realistic clouds is a lot easier than you might think at first. You might try putting a texture-mapped dome over the whole scene, but the perspective will be off when you move the camera. You might also try modelling individual clouds, but that would take up a big amount of memory. The best way I've found uses only one polygon with the following properites:

  • dimensions: 1 million meters by 1 million meters, square.
    1000 meters up, facing down.
  • color = 200 200 200
  • color texture: fractal noise, value = 100 100 100
    size = 2000 2000 2000, frequencies 3, contrast 1
  • luminosity = 100%
  • diffuse = 0% (any lights wouldn't affect clouds)
  • specular, reflectivity = 0%
  • transparency = 20%
  • transparency texture: fractal noise, value = 100%
    size = 1000 1000 1000, frequencies 5, contrast 2

Although the Earth isn't flat, it's so absolutely huge that it might as well be when you're sitting right on it. The big flat polygon is so big that it stretches almost to the horizon. It's less than a pixel away from the horizon, though, so it looks fine! Best of all, when you move the camera, the perspective stays exactly the same.

Here's an overhead view of the cloud texture:


If you're blessed with a newer version of Lightwave, you can have this:


Layering two transparency fractal noise maps, one bigger than the other, will make nice spread-out clouds, instead of uniformly-distributed clouds.
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