Provided by: gmt-common_5.4.5+dfsg-2_all bug


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


       grdblend  [  blendfile  |  grid1  grid2  ... ]  -Goutgrid [  -Iincrement ] [  -Rregion ] [
       -Cf|l|o|u ] [  -Nnodata ] [  -Q ] [  -Zscale ] [  -V[level] ] [  -W[z] ]  [  -fflags  ]  [
       -nflags ] [ -r ]

       Note: No space is allowed between the option flag and the associated arguments.


       grdblend reads a listing of grid files and blend parameters and creates a binary grid file
       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.  Any input grid that does not share the final output grid's node
       registration and grid spacing will automatically be  resampled  via  calls  to  grdsample.
       Note:  Due  to  the  row-by-row  i/o  nature of operations in grdblend we only support the
       netCDF and native binary grid formats for both input and output.


              outgrid is the name of the binary output grid file. (See GRID FILE FORMATS  below).
              Only  netCDF  and  native  binary  grid  formats are can be written directly. Other
              output format choices will be handled by reformatting the output once  blending  is

              x_inc  [and  optionally  y_inc]  is  the  grid spacing. Optionally, append a suffix
              modifier. Geographical (degrees) coordinates: Append m to indicate arc minutes or s
              to  indicate  arc  seconds.  If  one  of  the  units e, f, k, M, n or u is appended
              instead, the increment is assumed to be given in meter, foot,  km,  Mile,  nautical
              mile  or  US  survey  foot,  respectively,  and will be converted to the equivalent
              degrees longitude at the middle latitude of the region (the conversion  depends  on
              PROJ_ELLIPSOID).  If  y_inc  is given but set to 0 it will be reset equal to x_inc;
              otherwise it will be converted to degrees  latitude.  All  coordinates:  If  +e  is
              appended  then the corresponding max x (east) or y (north) may be slightly adjusted
              to fit exactly the given increment  [by  default  the  increment  may  be  adjusted
              slightly  to fit the given domain]. Finally, instead of giving an increment you may
              specify the number of nodes  desired  by  appending  +n  to  the  supplied  integer
              argument;  the  increment  is  then  recalculated  from the number of nodes and the
              domain. The resulting increment value  depends  on  whether  you  have  selected  a
              gridline-registered  or  pixel-registered  grid;  see App-file-formats for details.
              Note: if -Rgrdfile is used then the grid spacing has already been initialized;  use
              -I to override the values.

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
              Specify the region of interest.


              ASCII  file with one record per grid file to include in the blend.  Each record may
              contain up to  three  items,  separated  by  spaces  or  tabs:  the  gridfile  name
              (required),  the  -R-setting  for  the interior region (optional), and the relative
              weight wr (optional). In the combined weighting scheme, this  grid  will  be  given
              zero  weight  outside its domain, weight = wr inside the interior region, and a 2-D
              cosine-tapered weight between those end-members in the boundary strip. However,  if
              a  negative  wr  is given then the sense of tapering is inverted (i.e., zero weight
              inside its domain). If the inner region  should  instead  exactly  match  the  grid
              region  then  specify  a  -  instead  of  the -R-setting, or leave it off entirely.
              Likewise, if a weight wr is not specified we default to a  weight  of  1.   If  the
              ASCII blendfile file is not given grdblend will read standard input. Alternatively,
              if you have more than one grid file to blend and you wish (a) all  input  grids  to
              have  the  same  weight (1) and (b) all grids should use their actual region as the
              interior region, then you may simply list all the grids on the command line instead
              of  providing  a  blendfile.  You  must  specify  at  least  2 input grids for this
              mechanism to work. Any grid that is  not  co-registered  with  the  desired  output
              layout  implied  by  -R,  -I  (and -r) will first be resampled via grdsample. Also,
              grids that are not in netCDF or native binary format will first be reformatted  via

       -C     Clobber  mode:  Instead of blending, simply pick the value of one of the grids that
              covers a node. Select from the following modes: f for the first  grid  to  visit  a
              node;  o  for  the last grid to visit a node; l for the grid with the lowest value,
              and u for the grid with the uppermost value. For modes f  and  o  the  ordering  of
              grids  in  the  blendfile  will dictate which grid contributes to the final result.
              Weights and cosine tapering are not considered when clobber mode is active.

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

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

       -V[level] (more ...)
              Select verbosity level [c].

       -W[z]  Do not blend, just output the weights used for each node [Default makes the blend].
              Append z to write the weight*z sum instead.

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

       -f[i|o]colinfo (more ...)
              Specify data types of input and/or output columns.

       -n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more ...)
              Select interpolation mode for grids.

       -r (more ...)
              Set pixel node registration [gridline].

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              just use -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation  of  all  options,
              then exits.


       By  default  GMT  writes  out grid as single precision floats in a COARDS-complaint netCDF
       file format. However, GMT is able to produce grid files in many other commonly  used  grid
       file formats and also facilitates so called "packing" of grids, writing out floating point
       data as 1- or 2-byte integers. To specify the precision, scale and offset, the user should
       add  the  suffix =ID[+sscale][+ooffset][+ninvalid], where ID is a two-letter identifier of
       the grid type and precision, and scale and offset are optional scale factor and offset  to
       be applied to all grid values, and invalid is the value used to indicate missing data. See
       grdconvert and Section grid-file-format of the GMT Technical Reference  and  Cookbook  for
       more information.

       When  writing  a netCDF file, the grid is stored by default with the variable name "z". To
       specify another variable name varname, append ?varname to the file name. Note that you may
       need  to  escape  the special meaning of ? in your shell program by putting a backslash in
       front of it, or by placing the filename and suffix between quotes or double quotes.


       When the output grid  type  is  netCDF,  the  coordinates  will  be  labeled  "longitude",
       "latitude", or "time" based on the attributes of the input data or grid (if any) or on the
       -f or -R options. For example, both  -f0x  -f1t  and  -R90w/90e/0t/3t  will  result  in  a
       longitude/time grid. When the x, y, or z coordinate is time, it will be stored in the grid
       as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH in the gmt.conf file
       or on the command line. In addition, the unit attribute of the time variable will indicate
       both this unit and epoch.


       While the weights computed are tapered from 1 to 0, we are computing weighted averages, so
       if  there  is  only  a single grid given then the weighted output will be identical to the
       input.  If you are looking for a  way  to  taper  your  data  grid,  see  grdmath's  TAPER


       To  create a grid file from the four grid files piece_?.nc, giving them each the different
       weights, make the blendfile like this

     -R<subregion_1> 1
     -R<subregion_2> 1.5
     -R<subregion_3> 0.9
     -R<subregion_4> 1

       Then run

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

       To blend all the grids called MB_*.nc given them all equal weight, try

              gmt grdblend MB_*.nc -R<full_region> -I<dx/dy> -V


       While grdblend can process any number of files, it works by keeping those files open  that
       are  being  blended,  and  close  files  as  soon as they are finished.  Depending on your
       session, many files may remain open at the same time.  Some operating systems  set  fairly
       modest  default  limits  on  how many concurrent files can be open, e.g., 256.  If you run
       into this problem then you can change this limit; see your operating system  documentation
       for how to change system limits.


       gmt, grd2xyz, grdconvert, grdedit, grdraster, grdsample


       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe