Among other things, Tim Cook saw fit to write:

> I made a second function of the bathymetric data and added that to the
> earth isosurface, where the function with the topography is subtracted,
> since they're two files each with a full 256 shades of grey and it's a
> shame to not use that full amount by trying to combine the two images
> into one, which would reduce the vertical resolution by half.

Some time ago, before this new Blue Marble appeared, I got a full
bathymetric and elevation data file frome somewhere (I don't remember the
URL or the resolution, but it was acceptable[*]). The original data was a
binary no-header 16-bit file, which I converted to pgm with some effort
(involving using sox for getting the correct byte ending), as at that time
POV-Ray didn't support reading 16-bit PNG files... This all goes to say
that you can in theory combine everything in a 16-bit file without losing
resolution, or even get the whole thing with higher resolution.

[*] I may have the file somewhere and could put it in a server if someone is
interested.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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