The /FORMAT option governs how the data part (pixel values) of the
RGDATA file must be read by GreG. Fmt is a valid fortran format (default
is 10z8, the minimal way to encode real*4 data). code may be BY, R4, R8,
I4 or I2, depending if the data written in the file are BYtes, Real4,
Real8, Integer4 or Integer2. (The values in the GreG map will always be
Reals*4 after the read is done).