NAME

       grdblend  -  Blend  several partially over-lapping grids into one large
       grid

SYNOPSIS

       grdblend      blendfile       -Ggrdfile       -Ix_inc[m|c][/y_inc[m|c]]
       -Rwest/east/south/north[r] [ -Nnodata ] [ -Q ][ -Zscale ] [ -V ] [ -W ]
       [ -f[i|o]colinfo ]

DESCRIPTION

       grdblend reads a listing of gridded files and blend parameters and cre-
       ates  a  binary  grdfile by blending the other grids using cosine-taper
       weights.  grdblend will report if some of the nodes are not  filled  in
       with data. Such unconstrained nodes are set to a value specified by the
       user [Default is NaN].  Nodes with more than one value will be  set  to
       the weighted average value.

       blendfile
              ASCII  file  with  one  record  per  grid file to include in the
              blend. Each record must contain the gridfile name,  the  -R-set-
              ting  for the interior region, and the relative weight wr, sepa-
              rated by spaces or tabs.  In the combined weighting scheme, this
              grid will be given weight = zero outside its domain, weight = wr
              inside the interior region,  and  a  2-D  cosine-tapered  weight
              between  those  end-members in the boundary strip.  If the ASCII
              file is not given grdblend will read standard input.

       -G     grdfile is the name of the binary output grdfile.

       -I     x_inc [and optionally y_inc] is the grid spacing.  Append  m  to
              indicate minutes or c to indicate seconds.

       -R     xmin,  xmax,  ymin, and ymax specify the Region of interest. For
              geographic regions,  these  limits  correspond  to  west,  east,
              south,  and north and you may specify them in decimal degrees or
              in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r  if  lower  left
              and  upper  right map coordinates are given instead of wesn. The
              two shorthands  -Rg  -Rd  stand  for  global  domain  (0/360  or
              -180/+180  in longitude respectively, with -90/+90 in latitude).
              For calendar time coordinates you may either give relative  time
              (relative  to  the  selected  TIME_EPOCH  and  in  the  selected
              TIME_UNIT; append t to -JX|x), or  absolute  time  of  the  form
              [date]T[clock]  (append  T  to  -JX|x). At least one of date and
              clock must be present; the T is always required. The date string
              must  be  of  the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
              yyyy[-Www[-d]] (ISO week calendar), while the clock string  must
              be  of  the form hh:mm:ss[.xxx]. The use of delimiters and their
              type and positions must be as indicated  (however,  input/output
              and plotting formats are flexible).

OPTIONS

       -N     No  data. Set nodes with no input grid to this value [Default is
              NaN].

       -Q     Create a header-less gridfile suitable for use  with  grdraster.
              Requires  that the output gridfile is a native format (i.e., not
              netCDF).

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

       -W     Do  not  blend, just output the weights used for each node. This
              option is valid when only one input grid  is  provided  [Default
              makes the blend].

       -Z     Scale output values by scale before writing to file. [1].

       -f     Special  formatting  of  input  and output columns (time or geo-
              graphical data) Specify i(nput) or  o(utput)  [Default  is  both
              input  and output].  Give one or more columns (or column ranges)
              separated by commas.  Append T (Absolute calendar time), t (time
              relative  to  chosen TIME_EPOCH), x (longitude), y (latitude), g
              (geographic coordinate), or f (floating point) to each column or
              column range item.

EXAMPLES

       To  create  a grdfile from the four gridded files piece_?.grd, make the
       blendfile like this

       piece_1.grd -R<subregion_1> 1
       piece_2.grd -R<subregion_2> 1
       piece_3.grd -R<subregion_3> 1
       piece_4.grd -R<subregion_4> 1

       Then run

       grdblend blend.job -Gblend.grd -R<full_region> -I<dx/dy> -V

SEE ALSO

       gmt(l), grd2xyz(l), grdedit(l)



GMT4.0                            1 Oct 2004                       GRDBLEND(l)