function get_offsets,filename,gridname

;  this function reads the grid block offset values
;  from a MISR L1B2 data file (so the vdata name is
;  hardcoded)
;
;  NOTE:  the EOS_GD_BLKSOMOFFSET routine does not work
;  so the work around is using the vdata where the offset
;  values are stored

  hfid = HDF_OPEN (filename, /READ)
  vdref = HDF_VD_FIND(hfid, '_BLKSOM:'+gridname)
  vdid = HDF_VD_ATTACH(hfid, vdref, /READ)
  numrec = HDF_VD_READ(vdid, offsets)
  HDF_VD_DETACH, vdid
  HDF_CLOSE, hfid

  return, offsets
end