GRDZIP(l)                                               GRDZIP(l)

NAME

       grdzip - Pack/unpack short integer data grids

SYNOPSIS

       grdzip  [ infile] [ -C|D ] [ -Eendian ] [ -Foutfile ] [ -H
       ] [ -Iin_size ] [ -V ] [ -Xnx ] [ -Ynx ]

DESCRIPTION

       grdzip reads a binary short int grid  (or  GMT  short  int
       grid;  see -H) (or stdin) and encodes it using the d2zdxdy
       differences of the data.  These increments are stored in a
       packed  8/16/24/32-bit format that varies with the size of
       the increments.  grdzip takes advantage of the  fact  that
       many  data  sets are smooth, so the differences from point
       to point are small and can be stored in much less than  16
       bits.   The endianness of the calling computer is recorded
       at the start of the file  so  that  grdzip  can  make  any
       required  byte swapping during unpacking.  The packed data
       is written to file (or stdout) via the bzip2 i/o  library,
       resulting  in  superior  data  compression.  For technical
       details, see grdzip.c.

OPTIONS FOR COMPRESSION

       infile binary, short integer file in scanline  format  [we
              read stdin if no file is given].

       -C     Selects compression [Default].

       -F     Specifies output file [Default is stdout].

       -H     Input  file  has  a  GMT  header structure [Default
              assumes no header].

       -V     Report progress  and  final  statistics  to  stderr
              [Default is silent].

       -X     Number  of  data  columns,  i.e., points along each
              scanline (not needed if header is present).

       -Y     Number of data rows, i.e., scanlines   (not  needed
              if header is present).

EXAMPLES OF COMPRESSION

       To compress the global topography file etopo5.i2, try

       grdzip etopo5.i2 -V -X4321 -X2160 -Fetopo5.gbz

       To pack Sandwell and Smith's 2 min gravity img file really
       small, try

       grdzip grav7.2.img -V -X10800 -X6336 > grav7.2.img.gbz

       The combined packing and compression reduces this  131  Mb
       file to approximately 25% of its size.

OPTIONS FOR DECOMPRESSION

       infile Packed  file made by grdzip -C [we read stdin if no
              file is given].

       -D     Selects decompression [Default is compression].

       -E     Select desired  endian-ness  of  the  output  file.
              Choose B for big-endian, L for little-endian, O for
              the the original  endian-ness  on  the  originating
              machine,  or  H  for  the host-system's endian-ness
              [Default].

       -F     Specifies output file [Default is stdout].

       -I     If stdin is read we need the packed  file's  actual
              input size in order to report on expansion/compres­
              sion ratio.

       -V     Report progress  and  final  statistics  to  stderr
              [Default is silent].

EXAMPLES OF DECOMPRESSION

       To  unpack  the  packed Sandwell and Smith's 2 min gravity
       img used in the example above, and make sure it is written
       in big-endian format, try

       grdzip grav7.2.img.gbz -D -EB -V > grav7.2.img



                            1 Apr 2002                  GRDZIP(l)