size limits in GEMPLT GF driver?

Hi all - I seem to have bumped up against a size limit in the GEMPLT GF driver, which is maybe the physical size of my console. Is there a straightforward way to get around this?
The job at hand is to create fine-scale global base maps for use in other applications; I really want to end up with a raw file of unsigned bytes of value 0 or 1, so another driver would be fine as long as I can manipulate its output into a raw byte field on Unix (SGI), Mac, or PC. [Or is there a raw byte field driver?]
My apologies in advance if this is an old topic - just point me to the relevant thread. 

Regards,
George

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