Info in .grid3 headers:
   version number
   xdim ydim zdim
   north south east west top bottom
   ns_res ew_res tb_res
   zone 
   proj 
   type (1=short 2=int 3=float)
   min max (data values)

Info in .dspf headers:
   version number
   xdim ydim zdim
   min max
   lightmodel (1=flat 2=gouraud)
   number of thresholds
   array of threshold values
   data offset 
   lookup offset

Thu Mar 28 09:31:59 CST 1996
In process of eliminating use of .grid3 files, using
new 3dgrid format instead.