TeX, PDF and the GPS

Hello,

I'm always puzzled to see that TeX dimensions are limited to
5 3/4 meters. Is there such a limit in the pdf format ?

It is then impossible to typeset in full scale on the size of
a cinema screen or a theatre curtain

Conversely, it's frightening how precise TeX is with 5 nanometer
graduation. Relatively to 5,75 meters, this is on a thousand kilometers
distance, a resolution of a single micrometer ! Still better than the
GPS, for a long time yet

Is this choice of scaling explained by Knuth ?

Regards.