3D SEG-Y using external "Nav" file?

TomPopowski

I am wondering if anyone who works with 3D SEG-Y volumes has encountered volumes "in the wild" that get their X,Y trace coordinates from an external "Nav" file? In all of the cases I've seen, either

1. The text header or a "load sheet" ties 3 or 4 Inline/Xline coordinates to actual X,Y coordinates,
   
2. the trace headers have proper X,Y coordinate fields, or
   
3. both a & b
   

Admittedly, I only see volumes that others have difficulty loading, but I have yet to see a Nav file with a 3D survey and wonder whether it is worth supporting?

Thanks,
Tom