The texture is 3-dimensional, so it is possible to create cube planets or even planets with cut-out parts that still have surfaces that resemble the earth surface. The texture is not scalable, and is designed to be used with texture coordinates in the range -1.0 to 1.0, e.g. a unit sphere. Of course the world coordinates need not have the same order of magnitude.
ambient is a value between 0.0 and 1.0 which determines how much of the base color of a surface that is visible when it is not illuminated by any light source.
specular is a value between 0.0 and 1.0 which is the fraction of color specularly reflected.
c3 is the shininess of the surface where 0.0 is the most dull and 1.0 is the most shiny.
opacity describes the opacity of a surface. 0.0 means totally transparent, 1.0 means totally opaque. May be a list of red, green and blue opacity values or a single value to be used for all color channels. Optional, default is 1.0.