NAME

     grdreformat - Converting between different grdfile formats.


SYNOPSIS

     grdreformat         ingrdfile[=id[/scale/offset[/nanvalue]]]
     outgrdfile[=id[/scale/offset[/nanvalue]]]                  [
     -Rwest/east/south/north[r] ] [ -V ]


DESCRIPTION

     grdreformat reads a grdfile in one format and writes it  out
     using  another  format.   As an option the user may select a
     subset of the data to be written  and  to  specify  scaling,
     translation, and nan-value.

     ingrdfile
          The grdfile to be read.  Append format  =id  number  if
          not a standard GMT netcdf-based grdfile.  If id is set,
          you may optionally append scale and offset to scale the
          data  and  then add an offset.  If scale and offset are
          supplied you may also append  a  value  that  represent
          'not-a-number' (for floating-point grids this is unnec-
          cesary since  the  IEEE  NaN  is  used;  however  short
          integers need a value which means no data available.)

     outgrdfile
          The grdfile to be written.  Append format =id number if
          not a standard GMT netcdf-based grdfile.  If id is set,
          you may optionally append scale and offset to scale the
          data  and  then add an offset.  If scale and offset are
          supplied you may also append  a  value  that  represent
          'not-a-number' (for floating-point grids this is unnec-
          cesary since  the  IEEE  NaN  is  used;  however  short
          integers  need  a value which means no data available.)
          For format =id > 0 the size of the GMT grdheader  block
          is hsize = 896 bytes, and the total size of the file is
          hsize + nx * ny * item_size,  where  item_size  is  the
          size in bytes of each element (1, 2, 4).  Bit grids are
          stored using 4-byte integers, each holding 32 bits,  so
          for  these files the size equation is modified by using
          ceil (nx / 32) * 4 instead of nx.  For header and  grid
          details, see Appendix B.


OPTIONS

     -R   west, east, south, and  north  specify  the  Region  of
          interest.  To specify boundaries in degrees and minutes
          [and seconds], use the dd:mm[:ss] format.  Append r  if
          lower  left  and  upper right map coordinates are given
          instead of wesn.

     -V   Selects verbose mode, which will send progress  reports
          to stderr [Default runs "silently"].


EXAMPLES

     To create a 4-byte raw floating point grid from  the  netcdf
     file data.grd, try

     grdreformat data.grd ras_data.b4=1 -V

     To make a 2-byte short integer file, scale it  by  10,  sub-
     tract 32000, setting NaNs to -9999, do

     grdreformat values.grd shorts.i2=2/10/-32000/-9999 -V

     To create a Sun standard 8-bit rasterfile for  a  subset  of
     the  data file image.grd, assuming the range in image.grd is
     0-1 and we need 0-255, try

     grdreformat image.grd  -R-60/-40/-40/-30  image.ras8=3/255/0
     -V


SEE ALSO

     gmt(l), grdmath(l)