Thanks very much for the helpful replies.  I was running version 20.0; I upgraded to 20.04p11 and am now seeing the expected values in my Java program!

As my investigations proceed, I'll be sure to share my findings and musings with this mailing-list, in case anyone's curious. 

Once I have written a program that can take in the TGA produced by Fractint and spit out an ASCII GRID file, I'll begin producing and converting ASCII GRID tiles that I'll stitch together into a surface in the GIS software.  I think I'll start with a perfectly reasonable 3x3 mosaic of 1280 x 1024 images, just to get the conversion and stitching process figured out.  Once the process is solid, I'll up the ante and aim for, say, a total resolution of 32,768 x 32,768, and we'll see how the GIS software handles 1Gb+...

P.s. Very glad to see the FOTD still going, Jim!... How many years has it been?

Thanks again,
--
Cheers from Mr. Tumnus!

"Here... take my handkerchief."

Hoofing it bare-chested since 1974.