grdraster(1) GMT grdraster(1)
NAME
grdraster - Extract subregion from a binary raster and save as a GMT
grid
SYNOPSIS
grdraster [ filenumber | ^<i>atext pattern^<i>a ]
-Rregion [ -Ggrdfile ] [ -Iincrement ] [ -Jparameters ] [
-V[level] ] [ -bobinary ] [ -donodata ] [ -oflags ]
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 nath point. The output of
grdraster is either grid or pixel registered depending on the registra-
tion 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.
-Rwest/east/south/north[/zmin/zmax][+r][+uunit]
west, east, south, and north specify the region of interest, and
you may specify them in decimal degrees or in
[A+-]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. Appending +uunit expects projected (Carte-
sian) 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][+e|n][/yinc[unit][+e|n]]
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, nau-
tical mile or US survey foot, respectively, and will be con-
verted to the equivalent degrees longitude at the middle lati-
tude 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 coordi-
nates: 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 recalcu-
lated from the number of nodes and the domain. The resulting
increment value depends on whether you have selected a grid-
line-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 a|)
Select map projection.
-V[level] (more a|)
Select verbosity level [c].
-bo[ncols][type] (more a|)
Select native binary output.
-donodata (more a|)
Replace output columns that equal NaN with nodata.
-ocols[,a|] (more a|)
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 just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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.
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
SEE ALSO
gmtdefaults(1), gmt(1), grdsample(1), grdfilter(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 grdraster(1)
gmt5 5.4.2 - Generated Thu Jun 29 08:06:46 CDT 2017