Ubuntu Manpage: grdraster - Extract subregion from a binary raster and save as a GMT grid

Provided by: gmt-common_5.2.1+dfsg-3build1_all

NAME

       grdraster - Extract subregion from a binary raster and save as a GMT grid

SYNOPSIS

       grdraster  [  filenumber | "text pattern" ] region [ grdfile ] [ increment ] [ parameters ] [ [level] ] [
       -bo<binary> ] [ -do<nodata> ] [ -o<flags> ]

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

DESCRIPTION

       grdraster reads a file called grdraster.info from the current working directory, the directories  pointed
       to by the environment variables $GMT_USERDIR and $GMT_DATADIR, or in $GMT_SHAREDIR/dbase (in that order).
       The  file  grdraster.info  defines  binary arrays of data stored in scan-line format in data files.  Each
       file is given a filenumber in the info file. grdraster figures out how to load the  raster  data  into  a
       grid  file spanning a region defined by -R. By default the grid spacing equals the raster spacing. The -I
       option may be used to sub-sample the raster data. No filtering or interpolating  is  done,  however;  the
       x_inc  and  y_inc of the grid must be multiples of the increments of the raster file and grdraster simply
       takes every n'th point. The output of grdraster is either grid  or  pixel  registered  depending  on  the
       registration of the raster used. It is up to the GMT system person to maintain the grdraster.info file in
       accordance with the available rasters at each site. Raster data sets are not supplied with GMT but can be
       obtained  by  anonymous  ftp and on CD-ROM (see README page in dbase directory).  grdraster will list the
       available files if no arguments are given.  Finally, grdraster will write xyz-triplets to  stdout  if  no
       output gridfile name is given

REQUIRED ARGUMENTS

filenumber
If an integer matching one of the files listed in the grdraster.info file is given we will use
that data set, else we will match the given text pattern with the data set description in order to
determine the data set.

-R[unit]west/east/south/north[/zmin/zmax][r]
west, east, south, and north specify the region of interest, 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 w/e/s/n. The two shorthands -Rg and -Rd stand for global domain
(0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively for grid
creation, give Rcodelon/lat/nx/ny, where code is a 2-character combination of L, C, R (for left,
center, or right) and T, M, B for top, middle, or bottom. e.g., BL for lower left. This indicates
which point on a rectangular region the lon/lat coordinate refers to, and the grid dimensions nx
and ny with grid spacings via -I is used to create the corresponding region. Alternatively,
specify the name of an existing grid file and the -R settings (and grid spacing, if applicable)
are copied from the grid. Using -Runit expects projected (Cartesian) coordinates compatible with
chosen -J and we inversely project to determine actual rectangular geographic region. For
perspective view (-p), optionally append /zmin/zmax. In case of perspective view (-p), a z-range
(zmin, zmax) can be appended to indicate the third dimension. This needs to be done only when
using the -Jz option, not when using only the -p option. In the latter case a perspective view of
the plane is plotted, with no third dimension. If r is appended, you may also specify a map
projection to define the shape of your region. The output region will be rounded off to the
nearest whole grid-step in both dimensions.

OPTIONAL ARGUMENTS

       -Ggrdfile
              Name of output grid file. If not set, the grid will be written  as  ASCII  (or  binary;  see  -bo)
              xyz-triplets to stdout instead.

       -Ixinc[unit][=|+][/yinc[unit][=|+]]
              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 = 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 + 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.

       -Jparameters (more ...)
              Select map projection.

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

       -bo[ncols][type] (more ...)
              Select native binary output.

       -donodata (more ...)
              Replace output columns that equal NaN with nodata.

       -ocols[,...] (more ...)
              Select output columns (0 is first column).

         This option applies only if no -G option has been set.

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

       -+ 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 options, then exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

EXAMPLES

       To extract data from raster 1, taking one point every 30 minutes, in an area extended beyond 360  degrees
       to allow later filtering, run

              gmt grdraster 1 -R-4/364/-62/62 -I30m -Gdata.nc

       To  obtain  data  for  an oblique Mercator projection we need to extract more data that is actually used.
       This is necessary because the output of grdraster has edges defined by parallels and meridians, while the
       oblique map in general does not. Hence, to get all the data from the ETOPO2 data needed to make a contour
       map for the region defined by its lower left and upper right corners and the desired projection, use

              gmt grdraster ETOPO2 -R160/20/220/30r -Joc190/25.5/292/69/1 -Gdata.nc

       To extract data from the 2 min Geoware relief blend and write it as binary double precision  xyz-triplets
       to standard output:

              gmt grdraster "2 min Geoware" -R20/25/-10/5 -bo > triplets.b

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.2.1                                           January 28, 2016                                 GRDRASTER(1gmt)