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..::earth map::..

With all material emulation, your end result is only as good as the source material you use, so therefore search the Internet for reference photographs of the Earth from space. Nasa has a huge library of Earth photography taken from orbit, but bear in mind that each one differs from the next; the Sun may be in a different position, atmospheric conditions may be different and the camera position may be closer or further away from the atmosphere; all of which can alter the colour, contrast and brightness of the end result so choose carfully.

Viewing these photos we can observe that the Earth is not completely shiny; it varies depending on the surface being viewed. The sea is obviously highly refective, while ice-capped mountains are less so, down to the land which has virtually no value at all. Therefore a shininess map should be created to accomodate this; this should be an amended version of the main diffuse map with the sea having the highest value (ie closer to white) and the land the lowest (ie closer to black).

If viewing close to the surface, we will want to introduce a bump map to give the sea some texture; this noise procedural texture should be masked with another amended version of the main Earth map so everything apart from the sea is masked out. When creating outdoor scenes, additional realism can be added by adding fog atmospheric effects to desaturate the image the further the object is from the camera. The same principle applies here. Using a falloff map, the Earth map should be mixed with an additional map that has had all colour removed to generate this impression. This also give the impression of a living world with atmospheric conditions. Elements of habitation could be included as pinpoint lights where major cities and routes exist.

The clouds should cast shadows onto the surface, so you shouldn't really mix the cloud map(s) with the earth map(s). By creating a clone of the earth sphere and scaling it ever-so slightly, we can then apply our cloud material. However, a single opacity map will not suffice if the clouds are to be viewed at a close angle. Therefore, like the sea surface, a procedural noise or smoke map should be masked out with the cloud's opacity map as to give the appearance of depth when the camera is close to the cloud layer and is viewing them at an angle. This will also add additional detail to the map.

Finally, falloff should be introduced to give the impression of the thick atmosphere. This should be created to cover both earth and cloud spheres, so an additional clone of the earth sphere should be created and scaled to be just slightly bigger than the cloud sphere. A totally transparent material with no shininess applied with a fresnel map assigned to the opacity slot should be applied to the atmosphere sphere.

The end result is only as good as your materials and lighting (which should have a high soften edge, slight contrast and cast raytraced shadows to cast the cloud map's shadows); a good high quality earth map should be used and the same applies with the cloud map, but this can be an amalgamation of multiple maps to generate finer detail at close quarters. Finally, you may wish to slightly colourise the image slightly and amend the brightness and contrast by adding relevant render effects.

Enlarge ScreenshotThe individual components that build up the earth map and cloud layers
Enlarge ScreenshotThe final render with all elements applied to the three spheres that make up the final scene.

Initially published: 3D World magazine, Issue 19, December 2001.

Copyright Pete Draper, December 2001. Reproduction without permission prohibited.

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