PovRay planets, 25th of March 2012.
In computer graphics, texture is a description of the surface of an object. This includes:
- Surface appearance (color, patterns, pigments, transparency or partial transparency of the surface?)
- Surface reflectivity (does it behave like a mirror and in what percentage?)
- Relation of the surface to incoming light (how much of the received light is emitted diffusely by the object surface, is there some focusing in the scattered light so that one can see larger of smaller, more concentrated or diffuse trace of light on the object surface?)
- Surface "roughness" (it is the modification of the object normal by introducing noise or special function, which is taken into consideration when evaluating the relation of the object to the incoming light)
Without texture and its influence on the reflected light we could not judge objects which are of the same shape. Take, for example, spheres which are omnipresent shapes in the universe. Depending on the sphere texture, even when we do not know its size (i.e. its radius), we can, for example, differentiate between:
- lollipop (e.g. red sphere with a pattern of white lines)
- golf ball (white sphere with characteristic surface whose roughness is achieved by shallow spherical depressions; the surface is smooth on smaller scale so that it concentrates light in reflection)
- Ping-Pong ball (milky-white sphere, partly transparent, especially when viewed with a light source in the background, murky with respect to the reflection of light which is scattered quite diffusely, without a specularly enhanced shine)
- porcelain bead (I leave you to imagine this one)
- soap bubble (transparent sphere, partially reflective with a specularly enhanced shine and iridescence)
- chocolate pralines / dragees (e.g. with a hazelnut in the middle; chocolate-brown sphere with a diffusely enhanced glow, depending on the smoothness of the surface, i.e. on the chocolate temperature)
- pearl (e.g. black pearl - black, smooth and reflective sphere with a concentration of shine in reflection)
- fish egg or caviar
- star (e.g. Sun)
- planet
That's it - in no time I came from texture to planets. Using textures one can make fairly convincing planets. One such planet is shown in the image above. That planet is quite like our Earth. To make it, I used layered textures, i.e. several layers of textures applied one "above" the other. The texture layers need to be transparent in places so that below them one can see previously applied textures. The basic, ground level of texture can be completely opaque. In the case on the image above, I used special textures for
- land
- rivers
- oceans
- clouds
The textures were applied exactly in that order (land and the ground, basic texture, clouds as the topmost, mostly transparent texture). Layered composition of textures is a powerful procedure in computer graphics.
The planet above has a solid surface, but also a dense atmosphere which mostly obscures the surface. It looks to me as some poisonous place. Those who know a lot about spectroscopy could try to guess the chemical composition of the planet atmosphere from the analysis of its yellow color.
The planet above reminds me of a candy. It could be a gaseous giant. In contrast to the previous two planets, it focuses light in reflection, so that one can see a characteristic concentrated white shine.
The planet on the image above could be Solaris. Water world with a rare atmoshpere. God-child. To all who did not yet
read >> Lem's novel Solaris, I can warmly recommend it. I can also
recommend Soderbergh's movie >> Solaris which got some
quite bad reviews. I don't know why. I think that the movie excellently caught Lem's tempo and depressiveness and several
important aspects of the novel. George Clooney, whom I don't appreciate too much, was also excellent in the movie. Even Lem himself
criticized the movie, but that should not be taken to seriously - once the authors publish their works, they ceise to be exclusively
their ownership, so that Lem's opinion is important only to a certain extent. Of course, the movie could not cover all the
subtlety and span of Lem's writing - that would be absolutely impossible.
Note the unevenness of the reflection, especially in the region of the shine - this is meant to simulate the waves on the ocean surface.
Another variant of the water world is shown in the image above. This time the atmosphere is a bit denser and the clouds can be clearly seen.
The image above shows a liquid planet of lava in which pieces of "land" get solid and then melt again. Note that it emits light, which can be clearly seen in the region of the shadow. One can also note that the light is emitted only by liquid, orange parts of the planet surface.
A small step is separating the planet of lava and a star (image above). I included a lot of toroidal coronal loops in the model of the star.
In all examples thus far, the geometry of the surface was a perfect sphere, and all the effects were obtained by the texture. The image above shows the model of a moon which is not perfectly spherical. This is best seen in the shadow region. The effects obtained in this way is difficult (although not impossible) to simulate with the texture. PovRay has relatively powerful (but also slow) procedures for real modification of the object surface (these are the isosurface objects).
And in the end, the image above shows a piece of a moon, that was broken perhaps by a comet or an asteroid. The technique I used to create this object is the same as in the previous example (isosurface).
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Last updated on: 25th of March 2012.